44022-00-0898<90-00023> PAGE 7
The front panel INC CALL LED follows the ringing cycle. The
lamp lead and buzzer lead (pin 29) outputs also follow the ring-
ing cycle. In the order-wire application, the 46022 uses the
buzzer lead. Ringing is not applied.
♦The ring-back tone enable operates.
The ring-back tone enable operates an FET that allows the
ring-back tone from the 49920 ISM connected at pin 34 applies
to the transmit line. The ring-back tone also cycles by the in-
terrupt signal.
♦A 90 second timer starts.
The 90-second timer resets the module and transmits an on-
hook tone to the transmit circuit (back to the caller) if the
phone is not answered. The on-hook tone appears at pin 40. The
order-wire system does not use this capability.
The Ring Trip Sense Adjust compensates for situations where
system resistance exceeds the maximum loop loss. Do not use an
external ringing generator with the -00 option.
When an off-hook condition occurs during the ringing cycle, the
44022 detects the loop current, releases relay K1 and the front
panel OFF HOOK LED lights up.
The 44022 generates an off-hook tone enable which applies an off-
hook tone burst (100 milliseconds) to the transmit circuit (back to
the caller). The off-hook tone does not transmit in the order-wire
application.
The 44022 removes the ring-back and busy tone enables which:
♦Turns off their respective FETs.
♦Disables the 90 second timer.
♦Grounds the M lead at pin 21.
♦Establishes voice communication by flowing off-hook loop cur-
rent.
Clear Circuit
The clear function occurs when:
♦The phone hangs up.
♦90 seconds elapse during off-hook.
♦The call terminates before the phone answers.
When the phone hangs up, a pulse at the reset output (pin 3)
resets the 44020 DTMF Decoder Module and returns the circuit to
its normal condition.
Terminate a call before the phone answers by applying a ground to
the clear input (pin 16). Application of ground returns all functions
to normal and outputs a reset pulse at pin 3. The tone decoder
normally applies the clear input upon receipt of an on-hook tone.
CIRCUIT DESCRIPTION
