Motorola pro7100 Manuel de service télécharger pdf (Page 53)

Theory of Operation 2-39

The keypad back light current is drawn from the FLT A+ source and controlled by transistor Q0933.

The current flowing through the LED’s cause a proportional voltage drop across the parallel resistors

R0947, R0948. This voltage drop is amplified by the op-amp U0931-2. U0931-2 and Q0934 form a

differential amplifier. The voltage difference between the base of Q0934 and the output of U0931-2

determines the current from the base of the LED control transistor Q0933 and in turn the brightness

of the LED’s. The µP controls the LED’s by changing the dc level at the base of Q0934. If the base of

Q0934 is at ground level, Q0934 is switched off and no current flows through Q0933 and the LED’s.

If the base voltage of Q0934 rises a current flows through Q0934 and in turn through Q0933 causing

the LED’s to turn on and a rising voltage drop across R0947, R0948. The rising voltage causes the

output of the op-amp to rise and to reduce the base to emitter voltage of Q0934. This decreases the

current of Q0933 until the loop has settled.

2.11.7 Liquid Crystal Display (LCD)

The LCD H0971 uses the display driver U0971. The display is a single-layer super-twist pneumatic

(STN) LCD display. It has 14 characters with a 5*8 dot matrix for displaying 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 at

input SR2 (U0971-15). The driver’s internal oscillator is set to about 20 kHz and can be measured at

pin 22. The driver’s µP interface is configured to accept 8 bit parallel data input (U0971-D0-D7) from

the control head µP (U0831 port PC0-PC7).

To write data to the driver’s RAM the µP sets chip select (U0971-20) to logic 0 via U0831-11, RD

(U0971-18) to logic 1 via (U0831-10) and WR (U0971-17) to logic 0 via U0831-9. With input A0

(U0971-21) set to logic 0 via U0831-12 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, RD, and WD 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 external capacitors C0971 - C0973

configure the multiplier to double the supply voltage. In this configuration the multiplier output VOUT

(U0971-8) supplies a voltage of -5V (2* -5V below VDD). The multiplied voltage VOUT is sent to the

internal voltage regulator. To set the voltage level of the regulator output V5 (U0971-5) this voltage is

divided by the resistors R0973 and R0974 and fed back to the reference input VR (U0971-6). In

addition the regulator output voltage V5 can be controlled electronically by a control command sent

to the driver. With the used configuration the voltage V5 is about –2V. The voltage V5 is resistively

divided by the driver’s voltage follower to provide the voltages V1 - V4. These voltages are needed

for driving the liquid crystals. The level of V5 can be measured by one of the µP’s analog-to-digital

converters (U0831-20) via resistive divider R0975, R0976. To stabilize the display brightness over a

large temperature range the µP measures the temperature via analog-to-digital converter (U0831-

18) using temperature sensor U0834. Dependent on the measured temperature the µP adjusts the

driver output voltage V5, and in turn the display brightness, via parallel interface.

2.11.8 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.

1 2 ... 48 49 50 51 52 53 54 55 56 57 58 ... 108 109

Commentaires sur ces manuels

Pas de commentaire

Motorola pro7100 Manuel de service Page 53

Commentaires sur ces manuels

Produits connexes et manuels pour Récepteurs de médias en voiture Motorola pro7100