P
AGE
8
44023-1297 <90-00058>
When the 440 system site phone goes on hook, an on-hook tone
is decoded by the 44021. This causes the ground at pin 22 to be
removed, releasing the 44023 line seize logic to unbusy the 440
system. The 440 system is not busied by placing the outside
facility telephone on hook, unless the 44023 is strapped for
outside party control (Loop Control in)
The CCI circuit includes a 60-second fade delay timer. This
timer prevents a call from being disconnected should the radio
signal strength fade or a momentary interruption occur. The
44023 will disconnect from the outside call after one second if
the E lead ground is removed.
If an incoming ring signal is applied to the 44023 when the 440
system is internally busy, the 44023 will answer the incoming
call with a seven-second busy tone timer. The circuit will then
automatically disconnect the incoming call. The 44023 INC
CALL LED will come on for the duration of the seven-second
busy tone.
The transmit and receive mute FETs are unmuted when Q9 and
Q12 are switched on. This allows communications to proceed
when the 440 system phone is answered.
Outgoing Calls
An outgoing call from a system facility is initiated when a 440
system station telephone is lifted off hook. This transmits an
off-hook tone which causes the 44021 Address Decoder to ground
pin 22. The CCI (pin 18) must also be ground.
When the 440 system station telephone is taken off hook, the
440 system is busied out and the 44023 CKT BUSY LED
comes on. The calling party then dials the appropriate two- or
three-digit code to access the 44023 for the desired outside line.
When the last digit is dialed, the 44021 Address Decoder
grounds station call (pin 24) or group call (pin 26). The selected
call input (pin 24 or 26) is applied through a 400ms line seize
delay circuit. This delay prevents the last digit of the code dialed
from being tranmitted over the outside facility as the first digit
of an outgoing number.
When the call input is processed through the line seize logic Q12
turns on. This closes relay K1 and seizes the line. A ground
start strap option allows a momentary ground to be applied to
the tip (pins 44 and 46) to originate a call. Relay K2 switches the
M lead. The OFF HK LED comes on, the CKT BUSY LED goes
off, and the calling party receives a dial tone from the outside
facility. The calling party can now dial any desired outside
number.
When the outside call is terminated, a 0.2 second on-hook tone
burst from the 440 system is decoded by the 44021 Address
Decoder. This removes the ground from pin 22, which releases
the line seize logic and unbusies the 440 system.
CIRCUIT DESCRIPTION
