Microphone Connector Signals; Speaker; Electrostatic Transient Protection - Motorola CDM Series Detailed Service Manual

Control Head (CDM1250 / PRO5100 / CDM1550 Series / PRO7100)
These voltages are required to drive the liquid crystals. The level of V5 can be measured by one of
the µP's analog-to-digital converters (U0831-20) via resistive divider R0975, R0976. To stabilize the
display brightness over a large temperature range, the µP measures the temperature via analog-to-
digital converter (U0831-18) using temperature sensor U0834. Based on the measured
temperature, the µP adjusts the driver output voltage V5, and in turn the display brightness, via a
parallel interface.
3.8

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 accessories connected to the radio, if
any (for example, a microphone or a handset).
The two A/D converter inputs (J0811-9/10) are used for a microphone with a keypad. When a key is
pressed, the DC voltage changes on both lines. The voltages depend on which key is pressed. The
µP determines which key is pressed based on the voltage on these lines. It then sends the
information to the host radio.
Line PTT IRDEC (J0811-6) is used to key up the radio's transmitter. When 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 informs the host radio about any change
of status 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 the
radio on and puts the radio's µP in bootstrap mode. Bootstrap mode is the mode used to load the
firmware into the radio's flash memory (see the Controller chapter for more details).
The HOOK input (J0811-3) is used to signal the µP when the microphone's hang-up switch is
engaged. Depending on the CPS programming the µP may take actions like turning the audio PA on
or off. While the hang-up switch is open, line HOOK is pulled to 5V level by R0841. Transistor
Q0841 is switched on and causes a low at µP port PA1. When the HOOK switch is closed, signal
HOOK is pulled to ground level. This switches off R0841 and the resulting high level at µP port PA1
informs the µP about the closed hang-up switch. The µP will inform the host radio about any status
change on the HOOK line via SBEP bus.
3.9

Speaker

The control head contains a speaker for receiver audio. The receiver audio signal from the
differential audio output of the audio amplifier (located on the radio's controller) is fed via connector
J0801-10, 11 to the speaker connector P0801 pin 1 and pin 2. The speaker is connected to the
speaker connector P0801. The control head speaker can be disconnected if an external speaker
(connected through the accessory connector) is used.
3.10

Electrostatic Transient Protection

Electrostatic transient protection is provided for the sensitive components in the control head by
diodes VR0811, VR00812, and VR0816 – VR0817. The diodes limit any transient voltages to
tolerable levels. The associated capacitors provide Radio Frequency Interference (RFI) protection.
Section 2: 2-7
6881091C63-F