Motorola GM300 Series Selling Manual page 41

Accessory Connector
8.3.3 Voice PTT
If Voice PTT is asserted, the TX audio is routed from one of the microphone paths. CPS
programming defines whether the external voice PTT uses the internal or external (pin 2)
microphone audio path.
8.3.4 Data PTT
If data PTT is asserted, it is assumed that the external PTT is an electronic switch (e.g. a modem)
and that it requires the fastest possible radio response. When this pin is asserted the microphone
path is muted and the TX audio is routed from the Flat TX audio input (pin 5).
8.3.5 Voice & Data PTT
If voice and data PTT is asserted, it is assumed that the external PTT is an electronic switch that
requires the fastest possible radio response. The microphone path and the Flat TX audio input are
both enabled and the two signals are summed to form the TX signal. CPS programming defines
whether the external PTT uses the internal or external (pin 2) microphone audio path.
8.3.6 Mute Audio PA
When this input is asserted the audio PA (and speaker) is muted. When it is de-asserted, the audio
PA operates under normal software control and follow programmed squelch requirements.
8.3.7 Open RX Audio
When this input is asserted the received audio, or option board audio (if fitted), is routed through to
the audio PA (and speaker) independent of the normal squelch criteria.
8.3.8 Public Address Enable
When enabled, this feature allows the radio to act as a 'Public Address' system. An external switch
is connected to this pin. When this pin is asserted, the radio routes the internal or external mic audio
through to the Rx Audio (pins 7 and 11). A public address kit must be connected to the Rx audio
pins; this provides extra audio amplification and connection to an external speaker (eg mounted on
the roof of the car).
When the public Address pin is asserted and the mic PTT is pressed, the radio cannot receive calls.
When the Public Address pin is asserted but the mic PTT is not pressed, the radio can receive calls.
However, the Public Address pin must be de-asserted (ie the external Public Address switch moved
to OFF) before the user can reply to the call.
8.3.9 Call 1, Call 2, Call 3, Call 4
If one of call 1, call 2, call 3 or call 4 inputs is asserted, then its associated telegram is transmitted.
It provides the same functionality that is assigned to a call programmed on a button.
2-23