CML Microcircuits

COMMUNICATION SEMICONDUCTORS

CMX624

V.23 / Bell 202 Modem

 2003 CML Microsystems Plc

D/624/7 September 2003

Features

Applications

•••• V.23 / Bell 202 Compatible Modem

•••• Telephone Telemetry Systems

•••• Integrated DTMF Encoder

•••• Remote Utility Meter Reading

•••• Call Progress Tone Detection

•••• Security Systems/Cash Terminals

•••• Line Reversal and Ring Detector

•••• Industrial Control Systems

•••• Low Power Operation (2.7V)

•••• Pay-Phones

•••• Part of the CMX6x4 Modem Series

•••• Cable TV Set-Top Boxes

1.1

Brief Description

The CMX624 V.23 / Bell 202 modem is intended for use in any telephone based information and telemetry

system with low power requirements. Using FSK signalling, fast call set-up times and robust error resistant

transmission can be implemented by efficient low power circuits. The circuit can operate at 1200bps full

duplex over a 4-wire circuit or 1200 bps plus low speed data over a 2-wire circuit. Flexible line driver and

receive hybrid circuitry are integrated on chip requiring only passive external components to build a 2- or 4-

wire interface. A low impedance pull down output is provided for a hook relay.

Control of the device is via a simple high speed serial bus; this allows easy interfacing to a host

µController. The data transmitted and received by the modem is also transferred over the same high

speed serial bus. On-chip programmable Tx and Rx UARTs allow asynchronous data to be simultaneously

encoded and decoded. Either UART may be disabled to allow 8-bit raw data to be received or transmitted.

Any repetitive 8-bit data pattern can be sent without the controller having to reload data every 8 bits. All 16

DTMF combinations are available along with a single tone 'melody' mode. The ringing, 2100Hz, call

progress and data detectors included on the CMX624 make the set-up of a telephone call a simple matter

for the host µController.

In many data collection and telemetry systems low power consumption is important. The CMX624 features

a 'Zero Power' standby mode. Whilst in standby the ring detector continues to operate and will supply the

host µController with an interrupt when line reversal or ringing is detected. The CMX624 can operate on a

supply voltage between 3.0V and 5.5V across the full temperature range of -40°C to +85°C.

The CMX624 is pin compatible with the CMX644A V22 and Bell 212A modem also from CML.