V.23 Compatible Modem

FX604

© 1996 Consumer Microcircuits Limited

5

D/604/3

1.4

External Components

R1

100k

Ω

C1, C2

18pF

X1

3.579545MHz

C3

0.1

µF

C4

0.1

µF

Resistors

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

Figure 2 Recommended External Components for Typical Application

1.5

General Description

1.5.1

Xtal Osc and Clock Dividers

Frequency and timing accuracy of the FX604 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 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 significant rise in the supply

current drawn by FX604 as well as generating undefined states of the RXD, DET and RDYN outputs.