V23 / Bell 202 Modem
CMX624
1.4
External Components
R1
X1
100kΩ
3.579545MHz
C1, C2
C3, C4
C5
18pF
0.1µF
*
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.
2003 CML Microsystems Plc
6
D/624/7
CMLMICRO [ CML MICROCIRCUITS ]
