D/624/6 January 2001
• V.23 / Bell 202 Compatible Modem
• Integrated DTMF Encoder
• Call Progress Tone Detection
• Line Reversal and Ring Detector
• Low Power Operation (2.7V)
• Part of the CMX6x4 Modem Series
V.23/Bell 202 Modem
• Telephone Telemetry Systems
• Remote Utility Meter Reading
• Security Systems/Cash Terminals
• Industrial Control Systems
• 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.
© 2001 Consumer Microcircuits Limited