Micro-Controller; Xtal Oscillator; Lcd; Keypad - Motorola MCS 2000 Service Instructions Manual

Micro-controller

Xtal Oscillator

LCD

Backlight
Controller
Power Supplies
Display
Temperature
Sensor

Keypad

Backlight
Keypad
8-4 Control Heads
Micro-controller U0653 and Data Expander U0654 control the operation of
the Control Head. The µ C 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 µ C 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.
The xtal oscillator is built using on chip oscillator gates of the microprocessor.
The xtal is a standard 4 MHz ceramic resonator.
The backlight consists of 36 LEDs in model I and 48 LEDs in model J. 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.
LCD controller U0651 contains the default character set. On Control Head
model J the controller is expanded by the use of an LCD driver U0652. The
LCD controller is connected to the µ C via data bus PA0-PA7, while the control
and read/write (R/W) lines are connected via PB5 and PB7 respectively.
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 J) under µ C control via U0655. The µ C 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 µ C calculates the correction to the bias voltage and adjusts the duty
cycle of the PLMA output to U0655 accordingly.
Display (H0650) is a double layer super twist LCD display. Control Head model
I has one line of 14 characters with fixed symbols on top, six key-related
symbols on the bottom and RSSI symbol on the right-hand side. Control Head
model J is similar but has two lines of 14 characters. The presence of a rotary
switch tells the software that the display is a one-line display.
µ C U0653 measures voltage on PD7 which is controlled by dividers R0741 and
R0742. R0742 is an NTC resistor which is placed in close proximity to the LCD
display. The temperature sensor protects the backlight LEDs from failure and
is also used to compensate the LCD bias voltage dependent on the LCD glass
temperature. The protection temperature is 77 ° C ± 6 ° C.
The backlight consists of 7 LEDs in model I and 13 LEDs in model J. The
backlight can be switched on/off by the radio software, controlled via µ C
U0653 TCMP1 and TCMP2. A high pulse on TCMP1 turns on the backlight
and a low pulse on TCMP2 turns it off. If the temperature rises above 78 ° C in
the Control Head the µ C turns off the backlight utilising the Temperature
Sensor input.
The keypad is a passive input scanning matrix such that each key has 3 poles.
When a key is pressed a row and column are connected to ground and sensed