Status Led And Back Light Circuit; Microphone Connector Signals - Motorola CDM Series Detailed Service Manual

Control Head (CDM750 / PRO3100)
An additional pair of analog lines and A/D µP ports (PE 3 – 2) are 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 a control head.
2.6

Status LED and Back Light Circuit

All indicator LEDs (red, yellow, and green) are driven by current sources. To change the LED status
the host radio sends a data message via SBEP bus to the control head µP. The control head µP
determines the LED status from the received message and switches the LEDs 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 LEDs
using µP port PA 5. The µP can switch the back light on and off under software control. The back
light current for the keypad is drawn from the FLT A+ source and controlled by two 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 two 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. The 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 two A/D converter inputs (J0811-9/10) are used for a microphone with keypad. A pressed key
changes 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 5V 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 Q0843 off and the resulting high level at µP port
PA2 signals the µP about the pressed PTT button. The µP signals the host radio about any status
change on the PTT IRDEC line via SBEP bus.
When the 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 loads the firmware into the
radio's flash memory.
When the microphone's hang-up switch is engaged, the HOOK input (J0811-3) signals the µP.
Depending on how the radio is programmed using the Customer Programming Software (CPS), the
µP may take actions such as turning the audio PA on or off. While the hang-up switch is open,
R0841 pulls the line HOOK to a 5V level. Transistor Q0841 is switched on and causes a low at µP
port PA1. When the HOOK switch is closed, the HOOK signal is pulled to ground level. This
switches R0841 off and the resulting high level at µP port PA1 signals the µP about the closed
hang-up switch. The µP signals the host radio about any status change on the HOOK line via the
SBEP bus.
Section 2: 2-3
6881091C63-F