V22 and Bell 212A Modem

CMX644A

© 2000 Consumer Microcircuits Limited

6

D/644A/6

1.4

External Components

R1

100k

Ω *

C1, C2

18pF

X1

3.6864MHz, 7.372800MHz

or 11.0592MHz

C3, C4

C5

0.1

µF

1

µF

Resistors

±1%, capacitors ±20% unless otherwise stated.

* R1 should be selected so that the IRQN pin has returned to its normal

(high) state before the CSN pin goes high.

Figure 2 Recommended External Components for Typical Application

Notes on Xtal Osc and Clock Dividers

Frequency and timing accuracy of the CMX644A is determined by the 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 CMX644A.