Keypad; Mode Select; Multiplexer Operation - Motorola MCS 2000 Service Instructions Manual

Driver
Power Supplies
Display
Color Indicators

Keypad

Backlight
Keypad

Mode Select

Multiplexer
Operation
8-2 Control Heads
The LCD driver U0651 contains the default character set. Its interface is a four
line serial interface. The LCD driver is connected to the µ C on pins PA0 - PA3.
The driver has a built in oscillator with one external resistor, R0700, defining
the clock frequency. The oscillator runs at approx. 25 kHz giving an LCD frame
frequency of approx. 48 Hz.
The LCD driver and bias voltages are powered either from 5.0 V or 5.7 V. The
LCD bias voltage levels are created by the voltage divider R0701, R0702 and
R0703. This gives four voltages: supply voltage (VDD), V1, V2 and V3=GND.
The COM and SEG outputs from U651 jump between these 4 bias voltage
levels, which create the on and off AC voltage for each LCD segment.
Resistors R0715 and R0716 prevent U0651 from going into test mode during
power up.
The LCD supply voltage is controlled by the microcontroller U0653 PA6.
Display (H0650) is a transmissive/reflective positive LCD display. The Control
Head has one line of 8 characters with fixed symbols on top, four key-related
symbols on the bottom and three colour indicators.
The three color indicators are 4 LEDs D0679, D0680, D0681 and D0682. There
are two yellow LEDs in order to increase the colour intensity.
The keypad backlight is turned on and controlled along with the LCD
backlight.
The keypad is a static input with 10 kohms pull-up resistors. There is no
scanning, but simply one input for each key. Debouncing control is handled
by the software.
To reduce the number of pins on the microphone connector multiplexing is
utilised to switch between the 3 different modes, Normal mode, SB9600 mode
and Keyload mode.
The multiplexer comprises U0655 and U0656. Inputs to the multiplexer are
from the microphone connector pins 3, 6 and 7. The multiplexer is switched
either by a current sensing device (Q0662, Q0663), for Normal and SB9600 Bus
modes, or by software for keyload mode. Pin 1 of the microphone connector
carries the output current of the connected device.
When the output current is below 30 µ A, the multiplexer is switched to the
Normal mode.
When the connected device is an SB9600 device, the current is greater than 2
mA and the multiplexer is switched to SB9600 mode. Note that when an
SB9600 device is self-powered, i.e. no current consumption from the
microphone connector, a dummy load must be connected to pin 1 to ensure
a minimum current of 2 mA and force the multiplexer into the SB9600 mode.
A field programmer is an example of such a device.
In the Secure keyload mode, an A/D input on the µ C U0653 (PD6) monitors
the Speaker-output dc voltage.