Keypad Keys; Status Led And Back Light Circuit; Microphone Connector Signals - Motorola GM328 Service Manual

Controlhead Model for GM328
2.5

Keypad Keys

The controlhead keypad is a 6-key keypad. All keys are configured as 2 analogue lines read by µP
pins 13 and 15 . The voltage on the analogue lines varies between 0 volts and +5 volts depending on
which key has been pressed. If no key is pressed, the voltage at both lines will be 5 volts. The key
configuration can be thought of as a matrix, where the two lines represent one row and one column.
Each line is connected to a resistive divider powered by +5 volts. If a button is pressed, it will connect
one specific resistor of each divider line to ground level and thereby reduce the voltages on the
analogue lines The voltages of the lines are A/D converted inside the µP (ports PE 0 - 1) and specify
the pressed button. To determine which key is pressed, the voltage of both lines must be
considered.An additional pair of analogue lines and A/D µP ports (PE 3 – 2) is available to support a
keypad microphone, connected to the microphone connector J0811. Any microphone key press is
processed the same way as a key press on the controlhead.
2.6

Status LED and Back Light Circuit

All indicator LED's (red, yellow, green) are driven by current sources. To change the LED status the
host radio sends a data message via SBEP bus to the controlhead µP . The controlhead µP
determines the LED status from the received message and switches the LED's on or off via port PB
7 – 0 and port PA4. The LED status is stored in the µP 's memory. The LED current is determined by
the resistor at the emitter of the respective current source transistor.
The back light for the keypad is controlled by the host radio the same way as the indicator LED's
using µP port PA 5. The µP can switch the back light on and off under software control. The keypad
back light current is drawn from the FLT A+ source and controlled by 2 current sources. The LED
current is determined by the resistor at the emitter of the respective current source transistor.
2.7

Microphone Connector Signals

Signals BUS+, PTT IRDEC, HOOK, MIC, HANDSET AUDIO, FLT A+, +5V and 2 A/D converter
inputs are available at the microphone connector J0811. Signal BUS+ (J0811-7) connects to the
SBEP bus for communication with the CPS or the Universal Tuner. Line MIC (J0811-5) feeds the
audio from the microphone to the radio's controller via connector J0801-4. Line HANDSET AUDIO
(J0811-8) feeds the receiver audio from the controller (J0801-6) to a connected handset. FLT A+,
which is at supply voltage level, and +5V are used to supply any connected accessory like a
microphone or a handset.
The 2 A/D converter inputs (J0811-9/10) are used for a microphone with keypad. A pressed key will
change the dc voltage on both lines. The voltages depend on which key is pressed. The µP
determines from the voltage on these lines which key is pressed and sends the information to the
host radio.
Line PTT IRDEC (J0811-6) is used to key up the radio's transmitter. While the PTT button on a
connected microphone is released, line PTT IRDEC is pulled to +5 volts level by R0843. Transistor
Q0843 is switched on and causes a low at µP port PA2. When the PTT button is pressed, signal
PTT IRDEC is pulled to ground level. This switches off Q0843 and the resulting high level at µP port
PA2 informs the µP about the pressed PTT button. The µP will inform the host radio about any
status change on the PTT IRDEC line via SBEP bus.
When line PTT IRDEC is connected to FLT A+ level, transistor Q0821 is switched on through diode
VR0821 and thereby pulls the level on line ON OFF CONTROL to FLT A+ level. This switches on the
radio and puts the radio's µP in bootstrap mode. Bootstrap mode is used to load the firmware into
the radio's flash memory (See controller subsection for more details).
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