Evaluation Kit for CMX868

EV8680

© 2000 Consumer Microcircuits Limited

13

UM8680/2

1.6

Detailed Description

1.6.1

Hardware Description

1.6.1.1 Operating Voltage

R23 which are socketed. To select 2.7 Volts set R22 = 180

Ω and R23 = 100Ω. The formula for

calculating the values of R22 and R23 is as follows:

R22

R23

240 (V

1.25)

1.25

DD

+

=

−

multimeter.

1.6.1.3 Clock/Oscillator

The CMX868 may use either an external clock or its own crystal oscillator. An 11.0592MHz crystal is

provided on-board for the latter method. Two jumpers JP1 and JP2, which are normally fitted, select

the crystal oscillator. An external clock may be supplied to JP1 pin 2 once the jumpers have been

removed.

The PIC

µC is provided with an on-board 4MHz crystal, X2. Note that PICs programmed by CML are

only configured for use with the on-board 4MHz crystal.

1.6.1.4 Line Interface

The majority of the line interface components are fitted in sockets for adjustment purposes. These

values should be calculated based on the operating voltage and line conditions, see the CMX868 data

sheet and ETAL transformer recommendations for more information. The 2-wire ac line impedance

matching is provided by components C2, C4, R6, T1, C5, C8, R12 and R14 which are factory fitted to

suit a 600

Ω line.

A gyrator circuit is provided to allow the evaluation kit to be used with a line simulator. This circuit will

draw dc loop current in the off-hook state. The current drawn may be altered by adjusting the value of

R7. Note, the gyrator is designed to function with a dc current limited line.

1.6.1.5 Ring Detection

Ring Detection is provided by an opto-isolated circuit formed by components C1, D3 - D5, R5, R9 and

U2. The response time is set by components R10 and C6. See CMX868 data sheet for further

details.