TM8100 Mobile Radio Service Manual Circuit Descriptions 77
May 2004 © Tait Electronics Limited
Input Signals
(AUX GPI1 to AUX GPI3)
Dedicated inputs are provided on three pins of the auxiliary connector
(
AUX GPI1 to AUX GPI3). AUX GPI1 is a general-purpose input with strong
protection of the same type used for
AUX GPIO4. AUX GPI2 is normally a
dedicated emergency input but can be made a general-purpose input like
AUX GPI1 by removing the link LK3 in the power supply area. AUX GPI3 is
normally a dedicated ignition-sense input but can be made a general-
purpose input like
AUX GPI1 by removing the link LK2 in the power
supply area and fitting the 33 kΩ resistor R775.
ESD Protection 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
AUX GPIO4
this would consist of D713 and C725. The lines
IOP GPIO1 to IOP GPIO7
are intended for connection to internal digital devices and so these have
relatively light protection.
Hookswitch Detection 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
ITF CH HOOK line high; this indicates
either that the microphone is on hook or that the PTT (press-to-talk)
switch is pressed.
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