Keypad; Rotary Switch; Mode Select - Motorola MCS 2000 Service Instructions Manual

Control Heads: Models II and III
Display
Display (H0650) is a double layer super twist LCD display. Control Head model II 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 III 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.
Temperature Sensor
µC 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.

Keypad

Backlight
The backlight consists of 7 LEDs in model II and 13 LEDs in model III. The backlight can be switched
on/off by the radio software, controlled via µC 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 µC turns off the backlight utilizing the Temperature Sensor input.
Keypad
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 by the µC (PB0-PB4/PC0-PC4).
Only Control Head model III contains a full keypad.

Rotary Switch

Rotary switch R0697 (Control Head model II only) is a double wiper continuous turn 16-step
potentiometer. The two wipers are connected to two A/D inputs on the µC U0653 (PD1, PD2). One
input covers 8 steps from 0° to 180° and the other the 8 steps from 180° to 360°. The switch function
is software programmable and may be used for example to select shortform call numbers.

Mode Select

To reduce the number of pins on the microphone connector multiplexing is utilized to switch between
the 3 different modes, Normal mode, SB9600 mode and Keyload mode.
Multiplexer Operation
The multiplexer comprises U0657, U0658 and U0659. Inputs to the multiplexer are from the
microphone connector pins 3, 6 and 7. The multiplexer is switched either by a current sensing device
(Q0664, Q0665), 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 µA, 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.
68P81083C20-D
8-5
December 6, 2004