Liquid Crystal Display (Lcd); Microphone Connector Signals - Motorola MTM700 Detailed Service Manual

4.3 - 4
The µP can control the LED's by changing the dc level at the base of Q0943. If the base of Q0943 is
at ground level, Q0943 is switched off and no current flows through Q0941 and the LED's. If the
base voltage of Q0943 rises a current flows through Q0943 and in turn through Q0941 causing the
LED's to turn on and a rising voltage drop across R0955, R0957. The rising voltage causes the out-
put of the op-amp to rise and to reduce the base to emitter voltage of Q0943. This decreases the
current of Q0941 until the loop has settled.
The back light for the LCD module uses a similar circuitry. The only differences are that µP port PH2
controls the back light brightness and that the LED's are located on the LCD module which is con-
nected via J0821. Control line BL A GREEN connects to the anodes and control line BL K GREEN
connects to the cathodes of the LED's.

Liquid Crystal Display (LCD)

The LCD module consists of the display and the display driver and is connected via connector
J0821. The display is a single layer super twist nematic (STN) LCD display. It has a dot matrix of 32
* 96 dots for displaying graphics and alpha - numerical information and a line with 21 pre - defined
icons above the dot matrix
The driver contains a data interface to the µP, an LCD segment driver, an LCD power circuit, an
oscillator, data RAM and control logic. At power up the driver's control logic is reset by a logic „0" via
pin 5 of J0821. The driver's µP interface is configured to accept 8 bit parallel data input (J0821-D0-
D7) from the controlhead µP (U0871 port PC0-PC7).
To write data to the driver's RAM the µP sets chip select (J0821-6) to logic „0" via U0871-26, RD
(J0821-10) to logic „1" via (U0871-40) and WR (U0821-9) to logic „0" via U0871-33. With input A0
(J0821-8) set to logic „0" via U0871-34 the µP writes control data to the driver. Control data includes
the RAM start address for the following display data. With input A0 set to logic „1" the µP then writes
the display data to the display RAM. When data transfer is complete the µP terminates the chip
select and the clock activities.
The display driver's power circuit provides the voltage supply for the display. This circuit consists of
a voltage multiplier, voltage regulator and a voltage follower. The regulator output voltage for the dis-
play can be controlled electronically by a control command sent to the driver. The voltage level can
be measured by one of the µP's analogue to digital converters (U0871-42) via J0821-21. To stabilize
the display brightness over a large temperature range the µP measures the temperature via ana-
logue to digital converter (U0871-43) using a temperature sensor on the module (J0821-4). Depend-
ent on the measured temperature the µP adjusts the driver output voltage, and in turn the display
brightness, via parallel interface.

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 any connected accessory like a micro-
phone or a handset.
The 2 A/D converter inputs (J0811-9/10) are used for a microphone with keypad. A pressed key will
change the dc voltage on both lines. The voltages depend on which key is pressed. The µP deter-
mines from the voltage on these lines which key is pressed and sends the information to the host
radio.
MTM700 Mobile Radio / Detailed Service Manual THEORY OF OPERATION (CONTROL HEADS)