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CMX867A

Low Power

V.22 Modem

icrocircuits

COMMUNIC

ION SEMICONDUCTORS

D/867A/3 May

2008

Features

Applications

•

V.22, Bell 212A 1200/1200 or 600/600 bps DPSK

•

V.23 1200/75, 1200/1200, 75, 1200 bps FSK

•

Bell 202 1200/150, 1200/1200, 150, 1200 bps FSK

•

V.21 or Bell 103 300/300 bps FSK

•

Telephone Telemetry Systems

•

Remote Utility Meter Reading

•

Security Systems

•

Industrial Control Systems

•

Electronic Cash Terminals

•

Pay-Phones

•

DTMF/Tones Transmit and Receive

•

‘Powersave’ Standby Mode

•

Software and Hardware Compatible with CMX868A

•

Set-Top Boxes

Brief Description

The CMX867A is a multi-standard modem for use in telephone based information and telemetry systems.

Control of the device is via a simple high speed serial bus, compatible with most types of µC serial

interface. The data transmitted and received by the modem is also transferred over the same serial bus.

On-chip programmable Tx and Rx USARTs meeting the requirements of V.14 are provided for use with

asynchronous data and allow unformatted synchronous data to be received or transmitted as 8-bit words.

A high-quality DTMF decoder with excellent immunity to falsing on voice and a standard DTMF encoder

are included.

Alternatively, these blocks can be used to transmit and detect user-specific, programmed

single and dual-tone signals, call progress signals or modem calling and answering tones.

Flexible line driver and receive hybrid circuits are integrated on chip, requiring only passive external

components to build a 2 or 4-wire line interface.

The device also features a Hook Switch Relay Drive output and a Ring Detector circuit which continues to

function when the device is in the Powersave mode, providing an interrupt which can be used to wake up

the host µController when line voltage reversal or ringing is detected.

The CMX867A operates from a single 2.7 to 5.5V supply over a temperature range of -40°C to +85°C and

is available in 24-pin TSSOP, SOIC and DIP packages.

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CMX867A

CONTENTS

Section

Page

Brief Descriptio

………………………………………………………………………..

Block Diagra

……………………………………………………………………………

Signal Lis

………………………………………………………………………………….

External Components………………………………………………………………….

4.1

4.2

Ring Detector Interface ……………………………………………………

Line Interface…………………………………………………………………..

General Description…………………………………………………………………..

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

5.10

Tx USART………………………………………………………………………

FSK and DPSK Modulator

……………………………………………

Tx Filter and Equaliser …………………………………………………..

DTMF/Tone Generator ……………………………………………………

Tx Level Control and Output Buffer………………………………..

Rx DTMF/Tones Detector

…………………………………………….

Rx Modem Filtering and Demodulatio

………………………….

Rx Modem Pattern Detectors and Descrambler ………………

Rx Data Register and USART …………………………………………

C-BUS Interface……………………………………………………………..

5.10.1 General

Reset Comman

…………………………………..

5.10.2 General

Control Register ……………………………………

5.10.3 Transmit

Mode Registe

…………………………………….

5.10.4 Receive

Mode Register……………………………………….

5.10.5 Tx

Data Register…………………………………………………

5.10.6 Rx

Data Register ………………………………………………..

5.10.7 Status

5.10.8 Programming

Application Notes ……………………………………………………………………..

6.1

6.2

6.3

V.22 Calling Modem Application …………………………………….

V.22 Answering Modem Application……………………………….

Reference Diagrams ………………………………………………………

Performance Specification…………………………………………………………

7.1

Electrical Performanc

………………………………………………….

7.1.1 Absolute

Maximum Ratings………………………………..

7.1.2 Operating

Limits ………………………………………………..

7.1.3 Operating

Characteristics…………………………………..

Packaging ……………………………………………………………………..

7.2

It is always recommended that you check for the latest product datasheet version from the

Datasheets page of the CML website: [www.cmlmicro.com].

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CMX867A

Block Diagram

Figure 1

Block Diagram

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CMX867A

Signal List

CMX867A

D2/E2/P4

Signal

Name

Description

Pin No.

Type

XTALN

XTAL/CLOCK

RDRVN

O/P

The output of the on-chip Xtal oscillator inverter.

I/P

The input to the oscillator inverter from the Xtal

circuit or external clock source.

Relay drive output, low resistance pull down to

when active and medium resistance pull up

to V

when inactive.

O/P

Power

I/P

4, 8, 12, 17, 21

The negative supply rail (ground).

Schmitt trigger input to the Ring signal detector.

Connect to V

if Ring Detector not used.

Open drain output and Schmitt trigger input

forming part of the Ring signal detector. Connect

to V

if Ring Detector not used.

Power The

positive supply rail. Levels and thresholds

within the device are proportional to this voltage.

7, 16, 24

RXAFB

RXAN

RXA

O/P

The output of the Rx Input Amplifier.

I/P

The inverting input to the Rx Input Amplifier

The non-inverting input to the Rx Input Amplifier

I/P

BIAS

O/P

Internally generated bias voltage of

approximately V

/2, except when the device is

in ‘Powersave’ mode when V

BIAS

will discharge

to V

. Should be decoupled to V

by a

capacitor mounted close to the device pins.

The inverted output of the Tx Output Buffer.

TXAN

TXA

O/P

I/P

The non-inverted output of the Tx Output Buffer.

The C-BUS chip select input from the

The C-BUS serial data input from the

CSN

COMMAND

DATA

I/P

SERIAL

CLOCK

I/P

The C-BUS serial clock input from the

REPLY DATA

T/S

A 3-state C-BUS serial data output to the

This output is high impedance when not sending

data to the

IRQN

O/P

A ‘wire-ORable’ output for connection to a

Interrupt Request input. This output is pulled

down to V

when active and is high impedance

when inactive. An external pullup resistor is

required ie

R1 of Figure 2.

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Notes:

I/P

Input

O/P

T/S

Output

Bidirectional

3-state Output

No Connection

External Components

C1, C2

C3, C4

22pF

100nF

10uF

100k

11.0592MHz

or 12.288MHz

Resistors

5%, capacitors

20% unless otherwise stated.

Figure 2

Recommended External Components for a Typical Application

This device is capable of detecting and decoding small amplitude signals.

To achieve this V

and V

BIAS

should be decoupled and the receive path protected from extraneous in-band signals. It is recommended

that the printed circuit board is laid out with a V

ground plane in the CMX867A area to provide a low

impedance connection between the V

pins and the V

and V

BIAS

decoupling capacitors.

The V

connections to the Xtal oscillator capacitors C1 and C2 should also be low impedance and preferably be

part of the V

ground plane to ensure reliable start up of the oscillator.

For best results, an Xtal oscillator design should drive the clock inverter input with signal levels of at least

40% of V

peak-to-peak. Tuning-fork

Xtals generally cannot meet this requirement.

To obtain Xtal

oscillator design assistance, please consult your Xtal manufacturer.

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4.1

Ring Detector Interface

Figure 3 shows how the CMX867A may be used to detect the large amplitude Ringing signal voltage

present on the 2-wire line at the start of an incoming telephone call.

The ring signal is usually applied at the subscriber’s exchange as an ac voltage inserted in series with one

of the telephone wires and will pass through either C20 and R20 or C21 and R21 to appear at the top end

of R22 (point X in Figure 3) in a rectified and attenuated form.

The signal at point X is further attenuated by the potential divider formed by R22 and R23 before being

applied to the CMX867A RD input. If the amplitude of the signal appearing at RD is greater than the input

threshold (Vthi) of Schmitt trigger ‘A’ then the N transistor connected to RT will be turned on, pulling the

voltage at RT to V

by discharging the external capacitor C22. The output of the Schmitt trigger ‘B’ will

then go high, setting bit 14 (Ring Detect) of the Status Register.

The minimum amplitude ringing signal that is certain to be detected is:

( 0.7 + Vthi x [R20 + R22 + R23] / R23 ) x 0.707

Vrms

where Vthi is the high-going threshold voltage of the Schmitt trigger A (see section 7.1).

With R20-22 all 470k

as Figure 3, then setting R23 to 68k

will guarantee detection of ringing signals of

40Vrms and above for V

over the range 3 to 5V.

R20, 21, 22

R23

R24

C20, 21

C22

D1-4

470k

0.1

0.33

1N4004

See text

470k

Resistors

5%, capacitors

20%

Figure 3

Ring Signal Detector Interface Circuit

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If the time constant of R24 and C22 is large enough, then the voltage on RT will remain below the

threshold of the ‘B’ Schmitt trigger for the duration of a ring cycle.

The time for the voltage on RT to charge from V

towards V

can be derived from the formula

= V

x [1 – exp(-t/(R24 x C22)) ]

As the Schmitt trigger high-going input threshold voltage (Vthi) has a minimum value of 0.56 x V

, then

the Schmitt trigger B output will remain high for a time of at least 0.821 x R24 x C22 following a pulse at

RD.

The values of R24 and C22 given in Figure 3 (470k

and 0.33

F) give a minimum RT charge time of 100

msec, which is adequate for ring frequencies of 10Hz or above.

Note that the circuit will also respond to a telephone line voltage reversal. If necessary the

C can

distinguish between a Ring signal and a line voltage reversal by measuring the time that bit 14 of the

Status Register (Ring Detect) is high.

If the Ring detect function is not used then pin RD should be connected to V

and RT to V

4.2

Line Interface

A line interface circuit is needed to provide dc isolation and to terminate the line. Typical interface circuits

are described below.

2-Wire Line Interface

Figure 4a shows a simplified interface for use with a 600

2-wire line. The complex line termination is

provided by R13 and C10, high frequency noise is attenuated by C10 and C11, while R11 and R12 set

the receive signal level into the modem. For clarity the 2-wire line protection circuits have not been shown.

R11

R12

R13

See text

100k

600

C10

C11

See Figure 2

33nF

100pF

Resistors

5%, capacitors

20%

Figure 4a

2-Wire Line Interface Circuit

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Resistor R13 is used to match the AC impedance of the interface to the line. With an ideal transformer

this resistor would be equal to the desired impedance (e.g. 600

); however in practice with a real

transformer, R13 should be set such that the interface as a whole presents the desired impedance. Line

transformer manufacturers normally provide guidance in this regard.

The transmit line signal level is determined by the voltage swing between the TXA and TXAN pins, less

6dB due to the line termination, and less the loss in the line coupling transformer.

Allowing for 1dB loss in the transformer, then with the Tx Mode Register set for a Tx Level Control gain of

0dB the nominal transmit line levels will be:

= 3.0V

-10dBm

= 5.0V

-5.5dBm

QAM, DPSK and FSK Tx modes (no guard tone)

Single tone transmit mode

DTMF transmit mode

-6 and -8 dBm

-1.5 and -3.5 dBm

For a line impedance of 600

, 0dBm

= 775mVrms. See also section 7.1.3

In the receive direction, the signal detection thresholds within the CMX867A are proportional to V

and

are affected by the Rx Gain Control gain setting in the Rx Mode Register. The signal level into the

CMX867A is affected by the line coupling transformer loss and the values of R11 and R12 of Figure 4a.

Assuming 1dB transformer loss, the Rx Gain Control programmed to 0dB and R12 = 100k

, then for

correct operation (see section 7.1.3) the value of R11 should be equal to 500 / V

i.e. 160k

3.0V, falling to 100k

at 5.0V.

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4-Wire Line Interface

Figure 4b shows a simplified interface for use with a 600

4-wire line. The line terminations are provided

by R10 and R13, the values of which are dependent on the choice of transformer: see notes above. High

frequency noise is attenuated by C11 while R11 and R12 set the receive signal level into the modem.

Transmit and receive line level settings and the value of R11 are as for the 2-wire circuit.

R10, 13

R11

R12

See text

100k

C11

C12

See Figure 2

100pF

33nF

Resistors

5%, capacitors

20%

Figure 4b

4-Wire Line Interface Circuit

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General Description

The CMX867A transmit and receive operating modes are independently programmable.

The transmit mode can be set to any one of the following:

V.22 and Bell 212A modem. 1200 or 600 bps DPSK

(Differential Phase Shift Keying).

V.21 modem. 300bps FSK (Frequency Shift Keying).

Bell 103 modem. 300bps FSK.

V.23 modem. 1200 or 75 bps FSK.

Bell 202 modem. 1200 or 150 bps FSK.

DTMF transmit.

Single tone transmit (from a range of modem calling, answer and other tone frequencies)

User programmed tone or tone pair transmit (programmable frequencies and levels)

Disabled.

The receive mode can be set to any one of the following:

V.22 and Bell 212A modem. 1200 or 600 bps DPSK.

V.21 modem. 300bps FSK.

Bell 103 modem. 300 bps FSK.

V.23 modem. 1200 or 75 bps FSK.

Bell 202 modem. 1200 or 150 bps FSK.

DTMF detect.

2100Hz and 2225Hz answer tone detect.

Call progress signal detect.

User programmed tone or tone pair detect.

Disabled.

The CMX867A may also be set into a Powersave mode which disables all circuitry except for the C-BUS

interface and the Ring Detector.

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5.1

Tx USART

A flexible Tx USART is provided for all modem modes, meeting the requirements of V.14 for DPSK

modems.

It can be programmed to transmit continuous patterns, Start-Stop characters or Synchronous Data.

In both Synchronous Data and Start-Stop modes the data to be transmitted is written by the µC into the 8-

bit C-BUS Tx Data Register from which it is transferred to the Tx Data Buffer.

If Synchronous Data mode has been selected the 8 data bits in the Tx Data Buffer are transmitted serially,

b0 being sent first.

In Start-Stop mode a single Start bit is transmitted, followed by 5, 6, 7 or 8 data bits from the Tx Data

Buffer – b0 first – followed by an optional Parity bit then – normally – one or two Stop bits. The Start, Parity

and Stop bits are generated by the USART as determined by the Tx Mode Register settings and are not

taken from the Tx Data Register.

Figure 5a

Tx USART

Every time the contents of the C-BUS Tx Data Register are transferred to the Tx Data Buffer the Tx Data

Ready flag bit of the Status Register is set to 1 to indicate that a new value should be loaded into the C-

BUS Tx Data Register. This flag bit is cleared to 0 when a new value is loaded into the Tx Data Register.

Figure 5b

Tx USART Function (Start-Stop mode, 8 Data Bits + Parity)

If a new value is not loaded into the Tx Data Register in time for the next Tx Data Register to Tx Data

Buffer transfer then the Status Register Tx Data Underflow bit will be set to 1. In this event the contents of

the Tx Data Buffer will be re-transmitted if Synchronous Data mode has been selected, or if the Tx

modem is in Start-Stop mode then a continuous Stop signal (1) will be transmitted until a new value is

loaded into the Tx Data Register.

In all modes the transmitted bit and baud rates are the nominal rates for the selected modem type, with an

accuracy determined by the XTAL frequency accuracy, however for DPSK modes V.14 requires that

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Start-Stop characters can be transmitted at up to 1% overspeed (basic signalling rate range) or 2.3%

overspeed (extended signalling rate range) by deleting a Stop bit from no more than one out of every 8

(basic range) or 4 (extended range) consecutive transmitted characters.

To accommodate the V.14 requirement the Tx Data Register has been given two C-BUS addresses, $E3

and $E4. Data should normally be written to $E3.

In DPSK Start-Stop modes if data is written to $E4 then the programmed number of Stop bits will be

reduced by one for that character. In this way the µC can delete transmitted Stop bits as needed.

In FSK Start-Stop modes, data written to $E4 will be transmitted with a 12.5% reduction in the length of

the Stop bit at the end of that character.

In all Synchronous Data modes data written to $E4 will be treated as though it had been written to $E3.

The underspeed transmission requirement of V.14 is automatically met by the CMX867A as in Start-Stop

mode it automatically inserts extra Stop bit(s) if it has to wait for new data to be loaded into the C-BUS Tx

Data Register.

The optional V.22 compatible data scrambler can be programmed to invert the next input bit in the event

of 64 consecutive ones appearing at its input. It uses the generating polynomial:

-14

1 + x

-17

+ x

5.2

FSK and DPSK Modulators

Serial data from the USART is fed via the optional scrambler to the FSK modulator if V.21, V.23, Bell 103

or Bell 202 mode has been selected or to the DPSK modulator for V.22 and Bell 212A modes.

The FSK modulator generates one of two frequencies according to the transmit mode and the value of

current transmit data bit.

The DPSK modulator generates a carrier of 1200Hz (Low Band, Calling modem) or 2400Hz (High Band,

Answering modem) which is modulated at 600 symbols/sec as described below:

600bps V.22 signals are transmitted as a +90

carrier phase change for a ‘0’ bit, +270

for ‘1’.

For V.22 and Bell 212A 1200bps DPSK the transmit data stream is divided into groups of two

consecutive bits (dibits) which are encoded as a carrier phase change:

Dibit

(left-hand bit is the

Phase change

first of the pair)

+90

+270

+180

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5.3

Tx Filter and Equaliser

The FSK or DPSK modulator output signal is fed through the Transmit Filter and Equaliser block which

limits the out-of-band signal energy to acceptable limits. In 600 and 1200 bps FSK and DPSK modes this

block includes a fixed compromise line equaliser which is automatically set for the particular modulation

type and frequency band being employed. This fixed compromise line equaliser may be enabled or

disabled by bit 10 of the General Control Register. The amount of Tx equalisation provided compensates

for one quarter of the relative amplitude and delay distortion of ETS Test Line 1 over the frequency band

used.

5.4

DTMF/Tone Generator

In DTMF/Tones mode this block generates DTMF signals or single or dual frequency tones. In DPSK

modem modes it is used to generate the optional 550 or 1800Hz guard tone.

5.5

Tx Level Control and Output Buffer

The outputs (if present) of the Transmit Filter and DTMF/Tone Generator are summed then passed

through the programmable Tx Level Control and Tx Output Buffer to the pins TXA and TXAN. The Tx

Output Buffer has symmetrical outputs to provide sufficient line voltage swing at low values of V

and to

reduce harmonic distortion of the signal.

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5.6

Rx DTMF/Tones Detectors

In Rx Tones Detect mode the received signal, after passing through the Rx Gain Control block, is fed to

the DTMF / Tones / Call Progress / Answer Tone detector. The user may select any of four separate

detectors:

The DTMF detector detects standard DTMF signals. A valid DTMF signal will set bit 5 of the Status

The programmable tone pair detector includes two separate tone detectors (see Figure 10). The first

detector will set bit 6 of the Status Register for as long as a valid signal is detected, the second detector

sets bit 7, and bit 10 of the Status Register will be set when both tones are detected.

The Call Progress detector measures the amplitude of the signal at the output of a 275 – 665 Hz

bandpass filter and sets bit 10 of the Status Register to 1 when the signal level exceeds the measurement

threshold.

-10

-20

-30

-40

-50

-60

0.5

1.5

2.5

3.5

kHz

Figure 6a

Response of Call Progress Filter

The Answer Tone detector measures both amplitude and frequency of the received signal and sets bit 6

or bit 7 of the Status Register when a valid 2225Hz or 2100Hz signal is received.

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5.7

Rx Modem Filtering and Demodulation

When the receive part of the CMX867A is operating as a modem, the received signal is fed to a bandpass

filter to attenuate unwanted signals and to provide fixed compromise line equalisation for 600 and

1200bps FSK and DPSK modes. The characteristics of the bandpass filter and equaliser are determined

by the chosen receive modem type and frequency band. The line equaliser may be enabled or disabled

by bit 10 of the General Control Register and compensates for one quarter of the relative amplitude and

delay distortion of ETS Test Line 1.

The responses of these filters, including the line equaliser and the effect of external components used in

Figures 4a and 4b, are shown in Figures 6b-e:

-10

-20

-30

-40

-50

-60

-10

-20

-30

-40

-50

-60

0.5

1.5

2.5

3.5

0.5

1.5

2.5

3.5

kHz

Figure 6b

DPSK Rx Filters

Figure 6c

V.21 Rx Filters

-10

-20

-30

-40

-50

-60

-10

-20

-30

-40

-50

-60

0.5

1.5

2.5

3.5

0.5

1.5

2.5

3.5

kHz

Figure 6d

Bell 103 Rx Filters

Figure 6e

V.23/Bell 202 Rx Filters

The signal level at the output of the Receive Modem Filter and Equaliser is measured in the Modem

Energy Detector block, compared to a threshold value, and the result controls bit 10 of the Status

The output of the Receive Modem Filter and Equaliser is also fed to the FSK or DPSK demodulator

depending on the selected modem type.

The FSK demodulator recognises individual frequencies as representing received ‘1’ or ‘0’ data bits:

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The DPSK demodulator decodes DPSK modulation of a 1200Hz or 2400Hz carrier and is used for V.22

and Bell 212A modes. It includes an adaptive receive signal equaliser (auto-equaliser) that will

automatically compensate for a wide range of line conditions in DPSK modes. The auto-equaliser can

provide a useful improvement in performance in 600 or 1200bps DPSK modes, so although it must be

disabled at the start of a handshake sequence, it can be enabled as soon as scrambled 1200bps 1s have

been detected.

Both FSK and DPSK demodulators produce a serial data bit stream which is fed to the Rx pattern

detector, descrambler and USART block, see Figure 7a.

The demodulator input is also monitored for

continuous dibits ‘00,11’ in 1200bps DPSK mode and continuous alternating 1s and 0s in all other modes.

The DPSK demodulator also estimates the received bit error rate by comparing the actual received signal

against an ideal waveform. This estimate is placed in bits 2-0 of the Status Register.

5.8

Rx Modem Pattern Detectors and Descrambler

See Figure 7a.

The 1010.. pattern detector operates only in FSK modes and will set bit 9 of the Status Register when 32

bits of alternating 1’s and 0’s have been received.

The ‘Continuous Unscrambled 1’s’ detector operates in all modem modes and sets bits 8 and 7 of the

Status Register to ‘01’ when 32 consecutive 1’s have been received.

The descrambler operates only in DPSK modes and is enabled by setting bit 7 of the Rx Mode Register.

The ‘Continuous Scrambled 1’s’ detector operates only in DPSK modes when the descrambler is enabled

and sets bits 8 and 7 of the Status Register to ‘11’ when 32 consecutive 1’s appear at the output of the

descrambler. To

avoid possible ambiguity, the ‘Scrambled 1’s’ detector is disabled when continuous

unscrambled 1’s are detected.

The ‘Continuous 0’s’ detector sets bits 8 and 7 of the Status Register to ‘10’ when NX consecutive 0’s

have been received, NX being 32 except when DPSK Start-Stop mode has been selected, in which case

NX = 2N + 4 where N is the number of bits per character including the Start, Stop and any Parity bits.

All of these pattern detectors will hold the ‘detect’ output for 12 bit times after the end of the detected

pattern unless the received bit rate or operating mode is changed, in which case the detectors are reset

within 2 msec.

5.9

Rx Data Register and USART

A flexible Rx USART is provided for all modem modes, meeting the requirements of V.14 for DPSK

modems. It can be programmed to treat the received data bit stream as Synchronous data or as Start-

Stop characters.

In Synchronous mode the received data bits are all fed into the Rx Data Buffer which is copied into the

C-BUS Rx Data Register after every 8 bits.

In Start-Stop mode the USART Control logic looks for the start of each character, then feeds only the

required number of data bits (not parity) into the Rx Data Buffer. The parity bit (if used) and the presence

of a Stop bit are then checked and the data bits in the Rx Data Buffer copied to the C-BUS Rx Data

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Figure 7a

Rx Modem Data Paths

Whenever a new character is copied into the C-BUS Rx Data Register, the Rx Data Ready flag bit of the

Status Register is set to ‘1’ to prompt the µC to read the new data and, in Start-Stop mode, the Even Rx

Parity flag bit of the Status Register is updated.

In Start-Stop mode, if the Stop bit is missing (received as a ‘0’ instead of a ‘1’) the received character will

still be placed into the Rx Data Register and the Rx Data Ready flag bit set, but, unless allowed by the

V.14 overspeed option described below, the Status Register Rx Framing Error bit will also be set to ‘1’

and the USART will re-synchronise onto the next ‘1’ – ‘0’ (Stop – Start) transition.

The Rx Framing Error

bit will remain set until the next character has been received.

Figure 7b

Rx USART Function (Start-Stop mode, 8 Data Bits + Parity)

If the µC has not read the previous data from the Rx Data Register by the time that new data is copied to

it from the Rx Data Buffer then the Rx Data Overflow flag bit of the Status Register will be set to 1.

The Rx Data Ready flag and Rx Data Overflow bits are cleared to 0 when the Rx Data Register is read by

the µC.

For DPSK Start-Stop modes, V.14 requires that the receive USART be able to cope with missing Stop

bits; up to 1 missing Stop bit in every 8 consecutive received characters being allowed for the +1%

overspeed (basic signalling rate) V.14 mode and 1 in 4 for the +2.3% overspeed (extended signalling

rate) mode.

To accommodate the requirements of V.14, the CMX867A Rx Mode Register can be set for 0, +1% or

+2.3% overspeed operation in DPSK Start-Stop modes.

Missing Stop bits beyond those allowed by the

selected overspeed option will set the Rx Framing Error flag bit of the Status Register.

In order that received Break signals can be handled correctly in V.14 Rx overspeed mode, a received

character which has all bits ‘0’, including the Stop and any Parity bits, will always cause the Rx Framing

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Error bit to be set and the USART to re-synchronise onto the next ‘1’ – ‘0’ transition.

Additionally the

received Continuous 0s detector will respond when more than 2M + 3 consecutive ‘0’s are received,

where ‘M’ is the selected total number of bits per character including Stop and any Parity bits.

5.10

C-BUS Interface

This block provides for the transfer of data and control or status information between the CMX867A’s

internal registers and the µC over the C-BUS serial bus. Each transaction consists of a single Register

Address byte sent from the µC which may be followed by a one or more data byte(s) sent from the µC to

be written into one of the CMX867A’s Write Only Registers, or a one or more byte(s) of data read out from

one of the CMX867A’s Read Only Registers, as illustrated in Figure 8.

Data sent from the µC on the Command Data line is clocked into the CMX867A on the rising edge of the

Serial Clock input.

Reply Data sent from the CMX867A to the µC is valid when the Serial Clock is high.

The CSN line must be held low during a data transfer and kept high between transfers. The C-BUS

interface is compatible with most common µC serial interfaces and may also be easily implemented with

general purpose µC I/O pins controlled by a simple software routine. Figure 13 gives detailed C-BUS

timing requirements.

The following C-BUS addresses and registers are used by the CMX867A:

General Reset Command (address only, no data).

General Control Register, 16-bit write only.

Transmit Mode Register, 16-bit write-only.

Receive Mode Register, 16-bit write-only.

Transmit Data Register, 8-bit write only.

Receive Data Register, 8-bit read-only.

Status Register, 16-bit read-only.

Address $01

Address $E0

Address $E1

Address $E2

Addresses $E3 and $E4

Address $E5

Address $E6

Programming Register, 16-bit write-only.

Address $E8

Note: The C-BUS addresses $E9, $EA and $EB are allocated for production testing and should not be

accessed in normal operation.

5.10.1 General

Reset Command

General Reset Command

(no data)

C-BUS address $01

This command resets the device and clears all bits of the General Control , Transmit Mode and Receive

Mode Registers and bits 15 and 13-0 of the Status Register.

Whenever power is applied to the CMX867A, a General Reset command should be sent to the device.

This action will cause the device to enter a powersave state (General Control Register bit 8 will be cleared

to ‘0’). Note that the CMX867A does not automatically perform a power-on reset when power is first

applied.

To bring the device out of powersave, please refer to the description of bits 7 and 8 in the General Control

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Figure 8

C-BUS Transactions

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CMX867A

5.10.2 General

Control Register

General Control Register: 16-bit write-only.

C-BUS address $E0

This register controls general features of the CMX867A such as the Powersave and Loopback modes, the

IRQ mask bits and the Relay Drive output. It also allows the fixed compromise equalisers in the Tx and Rx

signal paths to be disabled if desired, and sets the internal clock dividers to use either a 11.0592 or a

12.288 MHz XTAL frequency.

All bits of this register are cleared to 0 by a General Reset command.

Bit:

TXA TXAN Xtal

off off

freq

Equ

Rly

drv

Pwr

Rst

Irqn

IRQ Mask Bits

General Control Register b15: Reserved, set to 0

General Control Register b14: Disconnect TXA Output

This bit allows the TXA output to be disconnected and set to high impedance.

b14 = 1

b14 = 0

TXA output disconnected.

TXA output connected (normal modem operation).

General Control Register b13: Disconnect TXAN Output

This bit allows the TXAN output to be disconnected and set to high impedance.

b13 = 1

b13 = 0

TXAN output disconnected.

TXAN output connected (normal modem operation).

General Control Register b12: Xtal frequency

This bit should be set according to the Xtal frequency.

b12 = 1

b12 = 0

11.0592MHz

12.2880MHz

General Control Register b11: Analogue Loopback test mode

This bit controls the analogue loopback test mode. Note that in loopback test mode both Transmit

and Receive Mode Registers should be set to the same modem type and band or bit rate.

b11 = 1

b11 = 0

Local analogue loopback mode enabled

No loopback (normal modem operation)

General Control Register b10: Tx and Rx Fixed Compromise Equalisers

This bit allows the Tx and Rx fixed compromise equalisers in the modem transmit and receive

filter blocks to be disabled.

b10 = 1

b10 = 0

Disable equalisers

Enable equalisers (600 or 1200bps modem modes)

General Control Register b9: Relay Drive

This bit directly controls the RDRVN output pin.

b9 = 1

b9 = 0

RDRVN output pin pulled to V

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General Control Register b8: Powerup

This bit controls the internal power supply to most of the internal circuits, including the Xtal

oscillator and V

BIAS

supply. Note that the General Reset command clears this bit, putting the

device into Powersave mode.

b8 = 1

b8 = 0

Device powered up normally

Powersave mode (all circuits except Ring Detect, RDRVN and C-BUS

interface disabled)

When power is first applied to the device,

the following powerup procedure should be

followed to ensure correct operation.

(Power is applied to the device)

ii.

iii.

Issue a General Reset command

Write to the General Control Register (address $E0) setting both the Powerup bit (b8)

and the Reset bit (b7) to ‘1’ – leave in this state for a minimum of about 20ms – it is

required that the crystal initially runs for this time in order to clock the internal logic into

a defined state.

The device is now powered up, with the crystal and V

BIAS

supply

operating, but is otherwise not running any transmit or receive functions.

The device is now ready to be programmed as and when required.

Examples:

iv.

•

A General Reset command could be issued to clear all the registers and therefore

powersave the device.

•

The Reset bit in the General Control Register could be set to ‘0’ as part of a routine

to program all the relevant registers for setting up a particular operating mode.

When the device is switched from Powersave mode to normal operation

by setting the

Powerup bit to ‘1’, the Reset bit should also be set to ‘1’ and should be held at ‘1’ for about 20ms

while the internal circuits, Xtal oscillator and V

BIAS

stabilise before starting to use the transmitter

or receiver.

General Control Register b7: Reset

Setting this bit to 1 resets the CMX867A’s internal circuitry, clearing all bits of the Transmit and

Receive Mode Registers and b13-0 of the Status Register.

b7 = 1

b7 = 0

Internal circuitry in a reset condition.

Normal operation

General Control Register b6: IRQNEN (IRQN O/P Enable)

Setting this bit to 1 enables the IRQN output pin.

b6 = 1

b6 = 0

IRQN pin driven low (to V

) if the IRQ bit of the Status Register = 1

IRQN pin disabled (high impedance)

General Control Register b5-0: IRQ Mask bits

These bits affect the operation of the IRQ bit of the Status Register as described in section

5.10.7

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5.10.3 Transmit

Mode Register

Transmit Mode Register: 16-bit write-only.

C-BUS address $E1

This register controls the CMX867A transmit signal type and level. All bits of this register are cleared to 0

by a General Reset command, or when b7 (Reset) of the General Control Register is 1.

Bit:

Tx mode = modem

Tx level

Guard tone

Scrambler

Start-stop /

synch data

# data bits /

synch data source

Tx mode = DTMF/Tones

Tx mode = Disabled

Tx level

DTMF Twist

Set to 0000 0000 0000

DTMF or Tone select

Tx Mode Register b15-12: Tx mode

These 4 bits select the transmit operating mode.

b15 b14 b13 b12

Do not use

V.22/Bell 212A 1200 bps DPSK

(Reserved for future use)

High band (Answering modem)

Low band (Calling modem)

High band (Answering modem)

Low band (Calling modem)

High band (Answering modem)

Low band (Calling modem)

High band (Answering modem)

Low band (Calling modem)

1200 bps

“

V.22 600 bps DPSK

“

V.21 300 bps FSK

“

Bell 103 300 bps FSK

“

V.23 FSK

“

Bell 202 FSK

“

DTMF / Tones

Transmitter disabled

75 bps

1200 bps

150 bps

Tx Mode Register b11-9: Tx level

These 3 bits set the gain of the Tx Level Control block.

b11

b10

0dB

-1.5dB

-3.0dB

-4.5dB

-6.0dB

-7.5dB

-9.0dB

-10.5dB

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Tx Mode Register b7-5: DTMF Twist (DTMF mode)

These 3 bits allow for adjustment of the DTMF twist to compensate for the frequency

response of different external circuits. Set b8 to 0. The device varies the twist by making

changes to the upper tone group levels. Note that the twist cannot be adjusted mid-tone.

+2.0dB twist (normal setting when external response is flat)

+1.0dB twist

+1.5dB twist

+2.5dB twist

+3.0dB twist

+3.5dB twist

+4.0dB twist

+4.5dB twist (do not use in conjunction with the 0dB tx level

setting).

Tx Mode Register b8-7: Tx Guard tone

(DPSK modes)

These 2 bits select the guard tone to be transmitted together with highband DPSK. Set

both bits to 0 in FSK modes.

Tx 550Hz guard tone

Tx 1800Hz guard tone

No Tx guard tone

Tx Mode Register b6-5: Tx Scrambler (DPSK modes)

These 2 bits control the operation of the Tx scrambler used in DPSK modes. Set both

bits to 0 in FSK modes.

Scrambler enabled, 64 ones detect circuit enabled (normal use)

Scrambler enabled, 64 ones detect circuit disabled

Scrambler disabled

Tx Mode Register b4-3: Tx Data Format (DPSK and FSK modes)

These two bits select Synchronous or Start-stop mode and the addition of a parity bit to

transmitted characters in Start-stop mode.

Synchronous mode

Start-stop mode, no parity

Start-stop mode, even parity bit added to data bits

Start-stop mode, odd parity bit added to data bits

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Tx Mode Register b2-0: Tx Data and Stop bits (DPSK and FSK: Start-Stop modes)

In Start-stop mode these three bits select the number of Tx data and stop bits.

8 data bits, 2 stop bits

8 data bits, 1 stop bit

7 data bits, 2 stop bits

7 data bits, 1 stop bit

6 data bits, 2 stop bits

6 data bits, 1 stop bit

5 data bits, 2 stop bits

5 data bits, 1 stop bit

Tx Mode Register b2-0: Tx Data source (DPSK and FSK: Synchronous mode)

In Synchronous mode (b4-3 = 11) these three bits select the source of the data fed to the Tx

FSK or DPSK scrambler and modulator.

Data bytes from Tx Data Buffer

Continuous 1s

Continuous 0s

Continuous dibits ’00,11’ in 1200bps DPSK mode, continuous

alternating 1s and 0s in all other modes.

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Tx Mode Register b8-0: DTMF/Tones mode

If DTMF/Tones transmit mode has been selected (Tx Mode Register b15-12 = 0001) then b8-5

should be set to 0000 and b4-0 will select a DTMF signal or a fixed tone or one of four

programmed tones or tone pairs for transmission.

b4 = 0: Tx fixed tone or programmed tone pair

b0 Tone

frequency (Hz)

No tone

697

770

852

941

1209

1336

1477

1633

1300

2100

2225

(Calling tone)

(Answer tone)

Programmed Tx tone or tone pair, see 5.10.8

Tone pair TA

Tone pair TB

Tone pair TC

Tone pair TD

“

b4 = 1: Tx DTMF

Low frequency (Hz)

High frequency (Hz)

Keypad symbol

941

697

770

852

941

697

770

852

1633

1209

1336

1477

1209

1336

1477

1209

1336

1477

1336

1209

1477

1633

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CMX867A

5.10.4 Receive

Mode Register

Receive Mode Register: 16-bit write-only.

C-BUS address $E2

This register controls the CMX867A receive signal type and level.

All bits of this register are cleared to 0 by a General Reset command, or when b7 (Reset) of the General

Control Register is 1.

Bit:

Rx mode = modem

Rx level

Descrambl

Start-stop/Synch

No. of bits and

parity

Rx mode = Tones detect

Rx mode = Disabled

Rx level

DTMF/Tones/Call Progress select

Set to 0000 0000 0000

Rx Mode Register b15-12: Rx mode

These 4 bits select the receive operating mode.

b15 b14 b13 b12

Do not use

V.22/Bell 212A 1200 bps DPSK

(Reserved for future use)

High band (Calling modem)

Low band (Answering modem)

High band (Calling modem)

Low band (Answering modem)

High band (Calling modem)

Low band (Answering modem)

High band (Calling modem)

Low band (Answering modem)

1200 bps

“

V.22 600 bps DPSK

“

V.21 300 bps FSK

“

Bell 103 300 bps FSK

“

V.23 FSK

“

75 bps

1200 bps

150 bps

Bell 202 FSK

“

DTMF, Programmed tone pair, Answer Tone, Call Progress detect

Receiver disabled

Rx Mode Register b11-9: Rx level

These three bits set the gain of the Rx Gain Control block.

b11

b10

0dB

-1.5dB

-3.0dB

-4.5dB

-6.0dB

-7.5dB

-9.0dB

-10.5dB

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Rx Mode Register b8: Rx Auto-equalise (DPSK modes)

This bit controls the operation of the receive DPSK auto-equaliser. Set to 0 in FSK modes.

b8 = 1

b8 = 0

Enable auto-equaliser

DPSK mode: Auto-equaliser disabled

Rx Mode Register b7-6: Rx Scrambler (DPSK modes)

These 2 bits control the operation of the Rx descrambler used in DPSK modes.

Set both

bits to 0 in FSK modes

Descrambler enabled, 64 ones detect circuit enabled (normal use)

Descrambler enabled, 64 ones detect circuit disabled

Descrambler disabled

Rx Mode Register b5-3: Rx USART Setting (DPSK and FSK modes)

These three bits select the Rx USART operating mode. The 1% and 2.3% overspeed options

apply to DPSK modes only.

Rx Synchronous mode

Rx Start-stop mode, no overspeed

Rx Start-stop mode, +1% overspeed (1 in 8 missing Stop bits allowed)

Rx Start-stop mode, +2.3% overspeed (1 in 4 missing Stop bits allowed)

Rx USART function disabled

Rx Mode Register b2-0: Rx Data bits and parity (DPSK and FSK: Start-Stop modes)

In Start-stop mode these three bits select the number of data bits (plus any parity bit) in each

received character. These bits are ignored in Synchronous mode.

8 data bits + parity

8 data bits

7 data bits + parity

7 data bits

6 data bits + parity

6 data bits

5 data bits + parity

5 data bits

Rx Mode Register b2-0: Tones Detect mode

In Tones Detect Mode (Rx Mode Register b15-12 = 0001) b8-3 should be set to 000000

Bits 2-0 select the detector type.

Programmable Tone Pair Detect

Call Progress Detect

2100, 2225Hz Answer Tone Detect

DTMF Detect

Disabled

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5.10.5 Tx

Data Register

Tx Data Register: 8-bit write-only.

C-BUS addresses $E3 and $E4

Bit:

Data bits to be transmitted

In Synchronous Tx data mode this register contains the next 8 data bits to be transmitted. Bit 0 is

transmitted first.

In Tx Start-Stop mode the specified number of data bits will be transmitted from this register (b0 first). A

Start bit, a Parity bit (if required) and Stop bit(s) will be added automatically.

This register should only be written to when the Tx Data Ready bit of the Status Register is 1.

C-BUS address $E3 should normally be used, $E4 is for implementing the V.14 overspeed transmission

requirement in Start-Stop mode, see section 5.1.

5.10.6 Rx

Data Register

Rx Data Register: 8-bit read-only.

C-BUS address $E5

Bit:

Received data bits

In unformatted Rx data mode this register contains 8 received data bits, b0 of the register holding the

earliest received bit, b7 the latest.

In Rx Start-Stop data mode this register contains the specified number of data bits from a received

character, b0 holding the first received bit.

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CMX867A

5.10.7 Status

Status Register: 16-bit read-only.

C-BUS address $E6

Bits 13-0 of this register are cleared to 0 by a General Reset command, or when b7 (Reset) of the

General Control Register is 1.

Bit:

IRQ

See below for uses of these bits

The meanings of the Status Register bits 12-0 depend on whether the receive circuitry is in Modem or

Tones Detect mode.

Status Register bits:

Rx Modem modes

Rx Tones Detect modes

** IRQ

Mask bit

b15

b14

b13

b12

IRQ

Set to 1 on

Ring Detect

Programming Flag bit. See 5.10.8

Set to 1 on Tx data ready.

Cleared by write to Tx Data Register

Set to 1 on Tx data underflow.

Cleared by write to Tx Data Register

b11

b10

1 when energy is detected in Rx

1 when energy is detected in Call

Progress band or when both

programmable tones are detected

modem signal band

1 when double DPSK dibit 00,11

pattern is detected in 1200bps

DPSK mode, or when ‘1010..’

pattern is detected in all other

modes

See following table

1 when 2100Hz answer tone or the

second programmable tone is

detected

Set to 1 on Rx data ready.

Cleared by read from Rx Data

Set to 1 on Rx data overflow.

Cleared by read from Rx Data

1 when 2225Hz answer tone or the

first programmable tone is detected

1 when DTMF code is detected

Set to 1 on Rx framing error

Set to 1 on even Rx parity

DPSK Rx signal quality b2

DPSK Rx signal quality b1

DPSK Rx signal quality b0

or FSK frequency demodulator

output

–

Rx DTMF code b3, see table

Rx DTMF code b2

Rx DTMF code b1

Rx DTMF code b0

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Notes: **

This column shows the corresponding IRQ Mask bits in the General Control Register. A 0 to 1

transition on any of the Status Register bits 14-5 will cause the IRQ bit b15 to be set to 1 if the

corresponding IRQ Mask bit is 1. The IRQ bit is cleared by a read of

the Status Register or a

General Reset command or by setting b7 or b8 of the General Control Register to 1.

The operation of the data demodulator and pattern detector circuits within the CMX867A does not

depend on the state of the Rx energy detect function.

Decoding of Status Register b8,7 in Rx Modem Modes, see also Figure 7a

b8 b7

Descrambler disabled

Descrambler enabled

(DPSK modes only)

Continuous scrambled 1s

(see note)

–

Continuous unscrambled 0s

Continuous unscrambled 1s

Continuous scrambled 0s

Continuous unscrambled

–

When the descrambler is enabled then detection of continuous unscrambled 1s will inhibit the

continuous scrambled 1s detector.

Figure 9a

Operation of Status Register bits 5-10

The IRQN output pin will be pulled low (to V

) when the IRQ bit of the Status Register and the

IRQNEN bit (b6) of the General Control Register are both 1.

Changes to Status Register bits caused by a change of Tx or Rx operating mode can take up to

150

s to take effect.

In Powersave mode or when the Reset bit (b7) of the General Control Register is 1 the Ring

Detect bit (b14) continues to operate.

The ‘continuous 0’ and ‘continuous 1’ detectors monitor the Rx signal after the DPSK

descrambler, (see Figure 7a) and hence will detect continuous 1s or 0s if the descrambler is

disabled, or continuous scrambled 1s or 0s if the descrambler is enabled.

In Rx FSK modem modes bits 2 and 1 will be zero and b0 will show the output of the frequency

demodulator, updated at 8 times the nominal data rate.

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Figure 9b

Operation of Status Register in DTMF Rx Mode

b3 b2 b1 b0 Low

frequency (Hz)

High frequency

(Hz)

Keypad symbol

941

697

770

852

941

697

770

852

1633

1209

1336

1477

1209

1336

1477

1209

1336

1477

1336

1209

1477

1633

Received DTMF Code: b3-0 of Status Register

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CMX867A

5.10.8 Programming

Programming Register : 16-bit write-only.

C-BUS address $E8

This register is used to program the transmit and receive programmed tone pairs by writing appropriate

values to RAM locations within the CMX867A. Note that these RAM locations are cleared by Powersave

or Reset.

The Programming Register should only be written to when the Programming Flag bit (b13) of the Status

programming action has been completed (normally within 150

s) the CMX867A will set the bit back to 1.

When programming Transmit or Receive Tone Pairs, do not change the Transmit or Receive Mode

Registers until programming is complete and the Programming Flag bit has returned to 1.

Transmit Tone Pair Programming

4 transmit tone pairs (TA to TD) can be programmed.

The frequency (max 3.4kHz) and level must be entered for each tone to be used.

Single tones are programmed by setting both level and frequency values to zero for one of the pair.

Programming is done by writing a sequence of up to seventeen 16-bit words to the Programming

The first word should be 32768 (8000 hex), the following 16-bit words set the frequencies and levels and

are in the range 0 to 16383 (0-3FFF hex)

Word

Tone Pair

Value written

32768

– – –

Tone 1 frequency

Tone 1 level

Tone 2 frequency

Tone 2 level

Tone 1 frequency

Tone 1 level

– – – – – – – – – –

Tone 2 frequency

Tone 2 level

The Frequency values to be entered are calculated from the formula:

Value to be entered = desired frequency (Hz) * 3.414

i.e. for 1kHz the value to be entered is 3414 (or 0D56 in Hex).

The Level values to be entered are calculated from the formula:

Value to be entered = desired Vrms * 93780 / V

i.e. for 0.5Vrms at VDD = 3.0V, the value to be entered is 15630 (3D0E in Hex)

Note that allowance should be made for the transmit signal filtering in the CMX867A which attenuates the

output signal for frequencies above 2kHz by 0.25dB at 2.5kHz, by 1dB at 3kHz and by 2.2dB at 3.4kHz.

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On powerup or after a reset, the tone pairs TA-TC are set to notone, and TD set to generate 2130Hz +

2750Hz at approximately –20dBm each.

Receive Tone Pair Programming

The programmable tone pair detector is implemented as shown in Figure 10a. The filters are 4

order IIR

sections. The frequency detectors measure the time taken for a programmable number of complete input

signal cycles and compare this time against programmable upper and lower limits.

Figure 10a

Programmable Tone Detectors

Figure 10b

Filter Implementation

Programming is done by writing a sequence of twenty-seven 16-bit words to the Programming Register.

The first word should be 32769 (8001 hex), the following twenty-six 16-bit words set the frequencies and

levels and are in the range 0 to 32767 (0000-7FFF hex).

Word Value

written

Word Value

written

32769

Filter #1 coefficient b2

Filter #1 coefficient b1

Filter #1 coefficient b0

Filter #1 coefficient a2

Filter #1 coefficient a1

Filter #1 coefficient b2

Filter #1 coefficient b1

Filter #1 coefficient b0

Filter #1 coefficient a2

Filter #1 coefficient a1

Filter #2 coefficient b2

Filter #2 coefficient b1

Filter #2 coefficient b0

Filter #2 coefficient a2

Filter #2 coefficient a1

Filter #2 coefficient b2

Filter #2 coefficient b1

Filter #2 coefficient b0

Filter #2 coefficient a2

Filter #2 coefficient a1

Freq measurement #1 ncycles

Freq measurement #1 mintime

Freq measurement #1 maxtime

Freq measurement #2 ncycles

Freq measurement #2 mintime

Freq measurement #2 maxtime

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The coefficients are entered as 15-bit signed (two’s complement) integer values (the most significant bit of

the 16-bit word entered should be zero) calculated as 8192 * coefficient value from the user’s filter design

program (i.e. this allows for filter design values of -1.9999 to +1.9999).

The design of the IIR filters should make allowance for the fixed receive signal filtering in the CMX867A

which has a low pass characteristic above 1.5kHz of 0.4dB at 2kHz, 1.2dB at 2.5kHz, 2.6dB at 3kHz and

4.1dB at 3.4kHz.

‘ncycles’ is the number of signal cycles for the frequency measurement.

‘mintime’ is the smallest acceptable time for ncycles of the input signal expressed as the number of

9.6kHz timer clocks. i.e. ‘mintime’ = 9600 *

ncycles / high frequency limit

‘maxtime’ is the highest acceptable time for ncycles of the input signal expressed as the number of

9.6kHz timer clocks. i.e. ‘maxtime’ = 9600 * ncycles / low frequency limit

The level detectors include hysteresis. The threshold levels – measured at the 2 or 4-wire line with unity

gain filters, using the line interface circuits described in section 4.2, 1.0 dB line coupling transformer loss

and with the Rx Gain Control block set to 0dB – are nominally:

‘Off’ to ‘On’

‘On’ to ‘Off’

-44.5dBm

-47.0dBm

Note that if any changes are made to the programmed values while the CMX867A is running in

Programmed Tone Detect mode they will not take effect until the CMX867A is next switched into

Programmed Tone Detect mode.

On powerup or after a reset, the programmable tone pair detector is set to act as a simple 2130Hz +

2750Hz detector.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Application Notes

6.1

V.22 Calling Modem Application

This section describes how the CMX867A can be used in a V.22 Calling modem application, employing

V.25 automatic answering and the V.22 recommended handshake sequence. This attempts to establish a

1200bps connection.

1. Ensure

that the CMX867A is powered up. Set the Tx Mode Register to DTMF/Tones mode (set to

‘No Tone’ at this time), and the Rx Mode Register to Call Progress Detect mode.

2. Connect

the line (go off hook) then dial the required number using the DTMF generator, monitoring

for call progress signals (dial tone, busy, etc). Change to Answer Tone Detect mode.

3. On

detection of the 2100Hz answer tone wait for it to end then wait for the 2225Hz answer tone

detector to respond.

(The ‘2225Hz’ answer tone detector will recognise unscrambled binary 1s at

1200bps High Band as well as 2225Hz).

When unscrambled binary 1s or 2225Hz have been

received for 155ms set a 456ms timer.

4. When

the 456ms timer expires check that the 2225Hz or unscrambled 1s is still being received, then

set the Tx Mode Register for V.22 1200bps Low Band transmission of scrambled 1s (continuous 1s

with the scrambler enabled).

Also set the Rx Mode register to V.22 1200bps High Band receive,

descrambler enabled and Rx USART disabled.

5. When

scrambled 1s (at 1200bps) have been received for 270ms enable the Rx USART, set a 765ms

timer and load the Tx Data Register with the first data to be transmitted.

6. When

the timer expires set the Tx Mode Register for Start-Stop or Synchronous transmission of data

from the Tx Data Buffer. This will start transmission of the data loaded in step 5.

7. A

1200bps data connection has now been established.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

6.2

V.22 Answering Modem Application

This section describes how the CMX867A can be used in a V.22 Answering modem application,

employing V.25 automatic answering and the V.22 recommended handshake sequence. This attempts to

establish a 1200 bps connection.

1. It

is assumed that the CMX867A will be in Powersave mode, with the Ring Detector circuits

monitoring the line.

2. When

a ring signal is detected connect the line (go off hook), set a 2150ms timer and power up the

CMX867A, setting the Tx Mode Register to DTMF/Tones mode (set for ‘no tone’ at this time) and the

Rx Mode Register to V.22 1200bps Low Band receive, descrambler enabled, Rx USART disabled.

3. When

the 2150ms timer expires set the Tx Mode Register to transmit the 2100Hz answer tone and

set a 3300ms timer.

4. When

the 3300ms timer expires set the Tx Mode Register to no tone and set a 75ms timer.

5. When

the 75ms timer expires set the Tx Mode Register for V.22 High Band 1200bps transmission of

unscrambled 1s. Monitor the received signal for scrambled 1s.

6. When

scrambled 1s have been detected for 270ms, set the Tx Mode Register to V.22 High Band

1200bps scrambled 1s transmission and set a 765ms timer and enable the Rx USART.

7. Load

the Tx Data Buffer with the first data to be transmitted.

8. When

the 765ms timer expires set the Tx Mode Register for Start-Stop or Synchronous transmission

of data from the Tx Data Buffer. This will start transmission of the data loaded in step 7.

9. A

1200bps data connection has now been established.

6.3

Reference Diagrams

The circuit diagrams in the DE8681 kit should be consulted for examples of a complete telephone line

interface. These

diagrams are contained in the DE8681 User Manual, which can be downloaded from the

CML website.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Performance Specification

7.1

Electrical Performance

7.1.1 Absolute

Maximum Ratings

Exceeding these maximum ratings can result in damage to the device.

Min.

Max.

7.0

+ 0.3

+50

+20

Units

Supply (V

– V

)

-0.3

-50

Voltage on any pin to V

Current into or out of V

and V

pins

Current into RDRVN pin (RDRVN pin low)

Current into or out of any other pin

-20

D2 Package

Total Allowable Power Dissipation at Tamb = 25°C

… Derating

Storage Temperature

Operating Temperature

Min.

Max.

600

6.0

+125

+85

Units

mW/°C

°C

-55

-40

°C

E2 Package

Total Allowable Power Dissipation at Tamb = 25°C

… Derating

Storage Temperature

Operating Temperature

Min.

Max.

1000

10.0

+125

+85

Units

mW/°C

°C

-55

-40

°C

P4 Package

Total Allowable Power Dissipation at Tamb = 25°C

… Derating

Storage Temperature

Operating Temperature

Min.

Max.

1660

16.6

+125

+85

Units

mW/°C

°C

-55

-40

°C

7.1.2 Operating

Limits

Correct operation of the device outside these limits is not implied.

Notes

Min.

2.7

-40

Max.

5.5

+85

Units

°C

Supply (V

– V

)

Operating Temperature

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

7.1.3 Operating

Characteristics

For the following conditions unless otherwise specified:

= 2.7V to 5.5V at Tamb = -40 to +85°C,

Xtal Frequency = 11.0592 or 12.288MHz

0.01% (100ppm)

0dBm corresponds to 775mVrms.

DC Parameters

(Powersave mode)

Notes

1, 2

1, 3

Min.

–

70%

–

-1.0

Typ.

2.0

1.7

2.5

3.0

5.5

–

Max.

–

3.5

5.0

6.0

11.0

–

Units

(Reset but not powersave, V

= 3.0V)

(Reset but not powersave, V

= 5.0V)

(Running, V

= 3.0V)

(Running, V

= 5.0V)

Logic ‘1’ Input Level

Logic ‘0’ Input Level

Logic Input Leakage Current (Vin = 0 to V

(excluding XTAL/CLOCK input)

Output Logic ‘1’ Level (l

= 2 mA)

Output Logic ‘0’ Level (l

= -3 mA)

IRQN O/P ‘Off’ State Current (Vout = V

and

RT pin Schmitt trigger input high-going

threshold (Vthi)

(see Figure 11)

RD and RT pin Schmitt trigger input low-going

threshold (Vtlo)

(see Figure 11)

–

30%

+1.0

80%

–

0.4

1.0

0.56V

+ 0.6V

0.44V

)

0.56V

0.44V

– 0.6V

–

RDRVN ‘ON’ resistance to V

= 3.0V)

RDRVN ‘OFF’ resistance to V

= 3.0V)

–

1300

3000

Notes:

1. At

C, not including any current drawn from the CMX867A pins by external circuitry

other than X1, C1 and C2.

2. All

logic inputs at V

except for RT and CSN inputs which are at V

3. General

Mode Register b8 and b7 both set to 1.

4. Excluding

RD and RT pins.

3.5

2.5

Vin

1.5

0.5

Vthi

Vtlo

2.5

3.5

4.5

5.5

Vdd

Figure 11

Typical Schmitt Trigger Input Voltage Thresholds vs. V

XTAL/CLOCK Input

Notes

Min.

Typ.

Max.

Units

(timings for an external clock input)

‘High’ Pulse Width

‘Low’ Pulse Width

–

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Transmit DPSK Modes

(V.22 and Bell 212A)

Notes

Min.

Typ.

Max.

Units

Carrier frequency, high band

Carrier frequency, low band

Baud rate

–

2400

1200

600

1200/600

550

-3.0

1800

-6.0

–

Baud

bps

Bit rate

–

550Hz guard tone frequency

550Hz guard tone level wrt data signal

1800Hz guard tone frequency

1800Hz guard tone level wrt data signal

548

-4.0

1797

-7.0

552

-2.0

1803

-5.0

Transmit V.21 FSK Mode

Baud rate

Mark (logical 1) frequency, high band

Space (logical 0) frequency, high band

Mark (logical 1) frequency, low band

Space (logical 0) frequency, low band

Notes

Min.

–

1647

1847

978

1178

Typ.

300

1650

1850

980

Max.

–

1653

1853

982

1182

Units

Baud

1180

Transmit Bell 103 FSK Mode

Baud rate

Mark (logical 1) frequency, high band

Space (logical 0) frequency, high band

Mark (logical 1) frequency, low band

Space (logical 0) frequency, low band

Notes

Min.

–

2222

2022

1268

1068

Typ.

300

2225

2025

1270

1070

Max.

–

2228

2028

1272

1072

Units

Baud

Transmit V.23 FSK Mode

Baud rate

Mark (logical 1) frequency, 1200 baud

Space (logical 0) frequency, 1200 baud

Mark (logical 1) frequency, 75 baud

Space (logical 0) frequency, 75 baud

Notes

Min.

–

1298

2097

389

449

Typ.

1200/75

1300

2100

390

Max.

–

1302

2103

391

451

Units

Baud

450

Transmit Bell 202 FSK Mode

Baud rate

Mark (logical 1) frequency, 1200 baud

Space (logical 0) frequency, 1200 baud

Mark (logical 1) frequency, 150 baud

Space (logical 0) frequency, 150 baud

Notes

Min.

–

1198

2197

386

486

Typ.

1200/150

1200

2200

387

Max.

–

1202

2203

388

488

Units

Baud

487

DTMF/Single Tone Transmit

Tone frequency accuracy

Distortion

Notes

Min.

-0.2

–

Typ.

–

1.0

Max.

+0.2

2.0

Units

Notes:

5. %

carrier frequency accuracy is the same as XTAL/CLOCK % frequency accuracy.

6. Tx

signal % baud or bit rate accuracy is the same as XTAL/CLOCK % frequency

accuracy.

7. Measured

between TXA and TXAN pins with Tx Level Control gain set to 0dB, 1k2

load

between TXA and TXAN, at V

= 3.0V (levels are proportional to V

– see section 4.2).

Level measurements for all modem modes are performed with random transmitted data

and without any guard tone. 0dBm = 775mVrms.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Transmit Output Level

Notes

Min.

-4.0

-2.0

Typ.

-3.0

-1.0

Max.

-2.0

0.0

Units

dBm

DBm

Modem and Single Tone modes

DTMF mode, Low Group tones

DTMF twist (level of high group tones wrt

low group) setting accuracy

-1.0

-0.25

–

+1.0

+0.25

Tx output buffer gain control accuracy

-10

Bell 202

-20

-30

dBm

-40

-50

-60

-70

100

1000

10000

100000

Figure 12

Maximum Out of Band Tx Line Energy Limits (see note 8)

Notes:

8. Measured

on the 2 or 4-wire line using the line interface circuits described in section 4.2

with the Tx line signal level set to -10dBm for DPSK, FSK or single tones, -6dBm and –

8dBm for DTMF tones. Excludes any distortion due to external components such as the

line coupling transformer.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Receive DPSK Modes

(V.22 and Bell 212A)

Carrier frequency (high band)

Carrier frequency (low band)

Baud rate

Notes

Min.

Typ.

Max.

Units

2392

1192

–

2400

1200

600

2408

1208

–

Baud

bps

Bit rate

1200/600

Receive V.21 FSK Mode

Acceptable baud rate

Mark (logical 1) frequency, high band

Space (logical 0) frequency, high band

Mark (logical 1) frequency, low band

Space (logical 0) frequency, low band

Notes

Min.

297

1638

1838

968

Typ.

300

1650

1850

980

Max.

303

1662

1862

992

Units

Baud

1168

1180

1192

Receive Bell 103 FSK Mode

Acceptable baud rate

Mark (logical 1) frequency, high band

Space (logical 0) frequency, high band

Mark (logical 1) frequency, low band

Space (logical 0) frequency, low band

Min.

297

2213

2013

1258

1058

Typ.

300

2225

2025

1270

1070

Max.

303

2237

2037

1282

1082

Units

Baud

Receive V.23 FSK Mode

1200 baud

Min.

Typ.

Max.

Units

Acceptable baud rate

Mark (logical 1) frequency

Space (logical 0) frequency

1188

1280

2080

1200

1300

2100

1212

1320

2120

Baud

75 baud

Acceptable baud rate

Mark (logical 1) frequency

Space (logical 0) frequency

382

442

390

450

398

458

Baud

Receive Bell 202 FSK Mode

1200 baud

Notes

Min.

Typ.

Max.

Units

Acceptable baud rate

Mark (logical 1) frequency

Space (logical 0) frequency

1188

1180

2180

1200

2200

1212

1220

2220

Baud

150 baud

Acceptable baud rate

Mark (logical 1) frequency

Space (logical 0) frequency

148

377

477

150

387

487

152

397

497

Baud

Rx Modem Signal

Notes

Min.

Typ.

Max.

Units

(FSK and DPSK Modes)

Signal level

Signal to Noise Ratio (noise flat 300-3400Hz)

-45

–

-9

–

dBm

Notes:

9. These

are the bit and baud rates of the line signal, the acceptable tolerance is ±0.01%.

10. Rx 2 or 4-wire line signal level assuming 1dB loss in line coupling transformer with Rx

Gain Control block set to 0dB and external components as section 4.2.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Rx Modem ‘0011’ Dibit

Pattern Detector

(1200bps DPSK mode)

Will detect pattern lasting for

Will not detect pattern lasting for

Hold time (minimum detector ‘On’ time)

Notes

Min.

90.0

5.0

Typ.

Max.

Units

–

72.0

–

Rx Modem Energy Detector

Detect threshold (‘Off’ to ‘On)

Undetect threshold (‘On’ to ‘Off’)

Hysteresis

Notes

10,11

Min.

–

-48.0

2.0

Typ.

Max.

-43.0

–

Units

dBm

–

Detect

(‘

Off’ to ‘On’) response time

DPSK modes

300 and 1200 baud FSK modes

150 and 75 baud FSK modes

10,11

10.0

8.0

16.0

–

35.0

30.0

60.0

Undetect

(‘

On’ to ‘Off’) response time

DPSK modes

300 and 1200 baud FSK modes

150 and 75 baud FSK modes

10,11

10.0

20.0

–

55.0

40.0

80.0

Rx Answer Tone Detectors

Detect threshold (‘Off’ to ‘On)

Undetect threshold (‘On’ to ‘Off’)

Hysteresis

Detect (‘Off’ to ‘On’) response time

Undetect (‘On’ to ‘Off’) response time

Notes

10,12

Min.

–

-48.0

2.0

30.0

7.0

Typ.

–

Max.

-43.0

–

Units

dBm

–

33.0

18.0

45.0

25.0

2100Hz detector

‘Will detect’ frequency

‘Will not detect’ frequency

2050

–

2160

2000

2225Hz detector

‘Will detect’ frequency

‘Will not detect’ frequency

2160

2335

–

2285

–

Rx Call Progress Energy Detector

Bandwidth (-3dB points)

See Figure 6a

Detect threshold (‘Off’ to ‘On)

Undetect threshold (‘On’ to ‘Off’)

Detect (‘Off’ to ‘On’) response time

Undetect (‘On’ to ‘Off’) response time

Notes

Min.

275

–

-42.0

30.0

6.0

Typ.

–

Max.

665

-37.0

–

45.0

50.0

Units

dBm

10,13

–

36.0

8.0

Notes:

11. Thresholds and times measured with random data for DPSK modes, continuous binary ‘1’

for all FSK modes. Fixed compromise line equaliser enabled. Signal switched between off

and -33dBm.

12. ‘Typical’ value refers to 2100Hz or 2225Hz signal switched between off and -33dBm.

Times measured wrt. received line signal.

13. ‘Typical’ value refers to 400Hz signal switched between off and -33dBm.

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

DTMF Decoder

Notes

Min.

Typ.

Max.

Unit

Valid input signal levels

(each tone of composite signal)

-31.0

–

2.0

dBm

Not decode level

(either tone of composite signal)

Twist = High Tone/Low Tone

Frequency Detect Bandwidth

Frequency Not Detect Bandwidth

Max level of low frequency noise (i.e dial tone)

Interfering signal frequency <= 550Hz

Interfering signal frequency <= 450Hz

Interfering signal frequency <= 200Hz

Max. noise level wrt. signal

DTMF detect response time

DTMF de-response time

Status Register b5 high time

‘Will Detect’ DTMF signal duration

‘Will Not Detect’ DTMF signal duration

Pause length detected

–

-10.0

±2.2

–

-37.0

10.0

–

dBm

±3.5

14,15

–

40.0

–

25.0

–

10.0

20.0

-10.0

–

30.0

–

15.0

–

14.0

40.0

–

30.0

–

Pause length ignored

Falsing performance

–

falses/

30mins

Notes:

14. Referenced to DTMF tone of lower amplitude.

15. Flat Gaussian Noise in 300-3400Hz band.

16. Mitel CM7291 test tape, 1kHz reference tone set to 775mVrms.

17. See Figure 9b. The decode time is directly affected by signal quality but, for good signals,

will always be much less than the 100ms required for PSTN use.

Receive Input Amplifier

Input impedance (at 100Hz)

Notes

Min.

10.0

Typ.

Max.

Units

Moh

Open loop gain

(at 100Hz)

Rx Gain Control Block accuracy

10000

V/V

-0.25

+0.25

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

C-BUS Timings (See Figure 13)

Notes

Min.

Typ.

Max.

Units

CSE

CSH

LOZ

CSN-Enable to Clock-High time

100

–

Last Clock-High to CSN-High time

100

0.0

–

Clock-Low to Reply Output enable

time

HIZ

CSN-High to Reply Output 3-state time

CSN-High Time between transactions

Inter-Byte Time

–

1.0

µs

CSOFF

NXT

1.0

–

200

100

75.0

25.0

50.0

0.0

Clock-Cycle time

Serial Clock-High time

Serial Clock-Low time

CDS

CDH

RDS

RDH

Command Data Set-Up time

Command Data Hold time

Reply Data Set-Up time

Reply Data Hold time

Maximum 30pF load on each C-BUS interface line.

Note: These timings are for the latest version of the C-BUS as embodied in the CMX867A.

Figure 13

C-BUS Timing

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

7.2

Packaging

Figure 14a

24-pin SOIC (D2) Mechanical Outline:

Order as part no. CMX867AD2

Figure 14b

24-pin TSSOP (E2) Mechanical Outline:

Order as part no. CMX867AE2

2008 CML Microsystems Plc

D/867A/3

Low Power V.22 Modem

CMX867A

Figure 14c

24-pin DIL (P4) Mechanical Outline:

Order as part no. CMX867AP4

Handling precautions:

This product includes input protection, however, precautions should be taken to prevent device damage

from electro-static discharge.

CML does not assume any responsibility for the use of any circuitry described.

No IPR or circuit

patent licences are implied.

CML reserves the right at any time without notice to change the said circuitry and this product

specification. CML

has a policy of testing every product shipped using calibrated test equipment to ensure compliance with this

product specification.

Specific testing of all circuit parameters is not necessarily performed.

CML-Microcircuits-CMX867AD2

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