Audio Configuration; Volume Control/On-Off; Micro-Controller; Xtal Oscillator - Motorola MCS 2000 Service Instructions Manual

8-4

Audio Configuration

The Control Head can be configured for Handset audio or Speaker+ which is a balanced output from
the radio. Handset audio is configured by inserting R0665 in the line from pin 8 to the microphone
connector. Speaker + audio is configured by inserting R0664 in the line from pin 1 to the microphone
connector. Note that only one resistor R0655 or R0644 must be fitted.

Volume Control/On-Off

Front panel switch/potentiometer R0696 controls the volume via A/D converter PD0 (pin 14) in
micro-controller (µC) U0653. The centre of the potentiometer is a push button switch used for
microphone input and power on-off. When activated the microphone line (pin 9) is connected to
ground.

Micro-controller

Micro-controller U0653 and Data Expander U0654 control the operation of the Control Head. The µC
exchanges data with the radio via the SB9600 bus (TD0 and RD1) and monitors inputs from the
microphone connector via the A/D port (PD0-PD7). In addition keypad and LCD data is processed
via ports A, B and C. Both the µC and the Expander are reset by under voltage detector U0660 when
Vcc drops below 4.6 V. Both devices can also be reset from the radio via the reset line (pin 3) and
Q0655.

Xtal Oscillator

The xtal oscillator is built using on chip oscillator gates of the microprocessor. The xtal is a standard
4 MHz ceramic resonator.

LCD

Backlight
The backlight consists of 36 LEDs in model II and 48 LEDs in model III. Light intensity is in 4 levels
including off and is software controlled by bus commands via Expander U0654 (Q6, Q7). A
temperature condition in the Control Head overrides the software commands such that on rising to
78°C or above the lowest light level or off is selected.
Controller
LCD controller U0651 contains the default character set. On Control Head model III the controller is
expanded by the use of an LCD driver U0652. The LCD controller is connected to the µC via data
bus PA0-PA7, while the control and read/write (R/W) lines are connected via PB5 and PB7
respectively.
Power Supplies
The LCD bias voltage drives the display segments. The bias voltage is divided into 5 levels by R0707
to R0711 and routed to the LCD controller (and LCD driver in Control Head model III) under µC
control via U0655. The µC measures the bias voltage with respect to Vcc (TP3) at A/D port PD3.
Another function of the bias voltage is temperature which is measured across R0742 at A/D port
PD7. The µC calculates the correction to the bias voltage and adjusts the duty cycle of the PLMA
output to U0655 accordingly.
December 6, 2004
Control Heads: Models II and III
68P81083C20-D