Kenwood TM-731A Service Manual page 13

TM-731A/E
CIRCUIT DESCRIPTION
¢ Reset and Backup Circuits R _
Fig. 17 shows the reset and backup circuits. ano soe LL
When power is switched on, the reset circuit applies a Low
Approx. 3 mS
pulse with a duration of approximately 3 mS to the RESET in-
put of the microprocessor. This causes a power-on reset. 33 Reset output
When power is. switched off, the backup circuit detects the I {at power-on)
voltage drop on the 8 V line and applies a High signal to the -t-q-4
INT4 input of the microprocessor. This places the microproces-
sor in the backup state. ¢
3
Backup circuit
Fig. 17 Reset and Backup Circuits
¢ Display Circuit
-- Located on-the LCD-assembly, the display circuit consists of a 50% duty cycle:-Fhe data-to-be-displayed is sent-as serial
two LCD drivers, one for the main band and one for the sub- data to the LCD from pins P30 to P33 of the microprocessor.
band, together with their supporting circuits and the liquid crys- In single operation, the microprocessor sends the subband LCD
tal display. (See Fig. 18.) The LCD is driven dynamically with driver an inhibit signal to suppress the subband display.
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Fig. 18 LCD Assembly (B38-0317-05)