Motorola GM340 Service-informatie - Pagina 17

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Controlhead Model for GM380, and GM1280

output 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

connected 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.

4.8

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

display 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

analogue to digital converter (U0871-43) using a temperature sensor on the module (J0821-4).

Dependent on the measured temperature the µP adjusts the driver output voltage, and in turn the

display brightness, via parallel interface.

4.9

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

microphone 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

determines from the voltage on these lines which key is pressed and sends the information to the

host radio.

Line PTT IRDEC (J0811-6) is used to key up the radio's transmitter. While the PTT button on a

connected microphone is released, line PTT IRDEC is pulled to +5 volts level by R0880. Transistor

Q0871 is switched on and causes a low at µP port PA2. When the PTT button is pressed, signal PTT

IRDEC is pulled to ground level. This switches off Q0871 and the resulting high level at µP port PA2

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