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R05

CPC7593

2.3.6 Break-Before-Make Operation Logic Table (Ringing to Talk Transition)

2.3.7 Alternate Break-Before-Make Operation

The second break-before-make method is also

available for use with all versions of the CPC7593. As

shown in “Truth Table for CPC7593xA and CPC7593xB” on

page 14 and “Truth Table for CPC7593xC and CPC7593xD”

of the CPC7593 switches when pulled to a logic low.

Although logically disabled, an active (closed) ringing

switch (SW4) will remain closed until the next current

zero crossing event.

As shown in the table “Break-Before-Make Operation

Logic Table (Ringing to Talk Transition)” on page 18, this

operation is similar to the one shown in “Alternate

Break-Before-Make Operation Logic Table (Ringing to Talk

Transition)” on page 19, except in the method used to

talk state.

1.

This opens the ringing return switch (SW3) and

prevents any other switches from closing.

2.

the ringing cycle period to allow sufficient time for

a zero crossing current event to occur and for the

circuit to enter the break before make state.

3.

(0,0,0).

4.

activate the break switches.

states are “0” which over rides logic input pins and

forces an all-off state and “Z” which allows switch

control via the logic input pins. This requires the use of

an open-collector or open-drain type buffer.

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

1

0

0

0Z

-Off

On

On

Off

10

1

Hold this state for at least

one-half of ringing cycle. SW4

waiting for zero current to turn

off.

Off

Off

On

Off

Break-

Before-

10

1

Zero current has occurred. SW4

has opened

Off

Off

Off

Off

Talk

0

0

0

Break switches close.

On

Off

Off

Off

* For the CPC7593xA/B versions the input pattern (1,1,1) may also be used for the all-off state.