Tait TM8000 Series Service Manual page 77

Input Signals
( 1 to
3)
AUX GPI AUX GPI
ESD Protection
Hookswitch Detection
TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
Dedicated inputs are provided on three pins of the auxiliary connector
1 to 3).
(
AUX GPI AUX GPI
protection of the same type used for
dedicated emergency input but can be made a general-purpose input like
1 by removing the link LK3 in the power supply area.
AUX GPI
normally a dedicated ignition-sense input but can be made a general-
purpose input like
AUX GPI
supply area and fitting the 33 kΩ resistor R775.
On exposed inputs of the auxiliary and control-head connectors ESD
(electrostatic discharge) protection is provided by a 470 pF capacitor and
by clamping diodes to ground and to 13.8 V. For example, on
this would consist of D713 and C725. The lines
are intended for connection to internal digital devices and so these have
relatively light protection.
Hookswitch detection is performed by Q700, R709, R706 and R712.
When the resistance to ground on the PTT line is less than 13.2 kΩ,
Q700 will turn on and drive the
either that the microphone is on hook or that the PTT (press-to-talk)
switch is pressed.
1 is a general-purpose input with strong
AUX GPI
AUX GPIO
1 by removing the link LK2 in the power
line high; this indicates
ITF CH HOOK
4. 2 is normally a
AUX GPI
AUX GPI
AUX GPIO
1 to
IOP GPIO IOP GPIO
Circuit Descriptions
3 is
4
7
77