V23 / Bell 202 Modem

CMX624

 2003 CML Microsystems Plc

6

D/624/7

1.4

External Components

R1

100k

Ω

C1, C2

18pF

X1

3.579545MHz

C3, C4

0.1

µF

C5

*

Resistors

±5%, capacitors ±10% unless otherwise stated.

* This component is only required for compatibility with CMX644A,

see CMX644A Data Sheet for further details.

Figure 2 Recommended External Components for Typical Application

1.5

General Description

The CMX624 contains a V.23/Bell 202 compatible FSK modem capable of duplex operation at 1200/75 or

1200/150 bps over a 2-wire line or 1200/1200 bps over a 4-wire line, a flexible FSK data UART, a receive

FSK or Call Progress Tone energy detector, a 2100Hz detector, a DTMF generator, a Tx line driving buffer

amplifier, a telephone line Ringing Signal or Line Voltage Reversal detector and a 3.579545MHz Xtal

oscillator. These functions are all controlled over a ‘C-BUS’ serial

µC interface which also carries the

transmit and receive FSK modem data.

1.5.1

Xtal Osc and Clock Dividers

Frequency and timing accuracy of the CMX624 is determined by a 3.579545MHz clock present at the

XTAL/CLOCK pin. This may be generated by the on-chip oscillator inverter using the external components

C1, C2 and X1 of Figure 2, or may be supplied from an external source to the XTAL/CLOCK input. If the

clock is supplied from an external source, C1, C2 and X1 should not be fitted.

The on-chip oscillator is turned off in the 'Zero-Power' mode.

If the clock is provided by an external source which is not always running, then the 'Zero-Power' mode

must be set when the clock is not available. Failure to observe this rule may cause a rise in the supply

current drawn by CMX624.