CPC5601

10

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R04

2.7 Operational Sequence

In the application circuits above, the CPC5601 is pow-

ered from the telephone line only when the LITELINK

is off-hook. This requires that you set the telephone

line characteristics controlled by the CPC5601 under

host system control immediately after taking the DAA

off-hook or after pulse dialing is complete, using the

following sequence:

1.

For incoming calls, validate a ring signal by hav-

ing the host system poll or read the output of

RING (ring detect via snoop circuit on the LITE-

LINK) or RING (ring detect via opto-isolated ring

circuit in the CPC5601).

2.

Assert OH to complete the connection.

3.

Set the telephone line characteristics of the DAA

using the CPC5601 via the programming method

(see “Programming” on page 10).

With this circuit, you must program the CPC5601 as

soon as possible after asserting off hook. Leaving the

CPC5601 unprogrammed leaves open the possibility

of LITELINK instability due to lack of AC termination.

2.8 Output Current Ratings

Output b6 is the only output that can be used for the

current limiting function of a DAA. The FET on output

b6 can sink up to 120 mA of current, while the other

outputs can sink up to 10 mA.

The other outputs can be used for any of the other

switchable functions on the telephone line side of a

DAA, as long as the current does not exceed the

10 mA limit.

3. Programming

3.1 Latch Circuit Description

Data applied to the input pin is optically coupled to the

shift register through a pulse generator. Each low-to-

high transition in the pulse generator triggers a clock

pulse. Clock pulses are applied to the CLK input of six

rising-edge-triggered flip-flops. The non-inverted input

data is fed to the flip-flops at all times, but the flip-flops

are only clocked on receipt of a pulse from the pulse

generator. The flip-flops drive six FET switches.