Power Supply Circuit - Sharp ER-A440 Service Manual

2) Power off sequence
When the CPU senses a service interruption, it performs necessary
procedures for CPU stop. Then the CPU outputs a reset request to
the CKDC5.
Reset request
SHEN DON'T CARE
SCK
LDRQ
RES1
When the CPU senses a service interruption or an error, it performs
necessary procedure for CPU stop and issues reset request.
CPU procedures necessary for reset request
All CPU interrupts are made DI.
SCK is driven to low.
Keep LDRQ at LOW level for 20usec or more and drive it HIGH.
Loop to . During looping, access should not be made to
external memory.
It should be within 140usec from rising of one LDRQ to rising of
another.
When, however, the CKDC8 senses a service interruption at POF, it
stops displaying. Service interruption procedure is performed after
receiving reset request from the CPU. If reset request is not sent from
the CPU within 100msec the service interruption procedure is started
after 110 10msec to go into the stand-by mode.
POF
RES1
3) Key and switch scanning
ST0
38µsec
ST9
KR0~KR7
KR10,KR11
As the strobe signal, 8 bits of ST0 - 8 are used.
KR0 - KR7 are used as the key return signal. KR10 is used as the
return signal of the paper feed key, cashier key and MRS switch.
KR11 is used as the return signal of the mode switch.
TL 20µsec or more
TH 20µsec or more
< =
TL+TH 140µsec
Fig. 9-3
110±10msec
Fig. 9-4
356.25µsec
Fig. 9-5
4) DISPLAY CONTROL
G1-G10
SA-SG,DP
CKDC5
CKDC8 directly drives the LED display unit.

10. Power supply circuit

Power
trans.
DC-DC
Converter
circuit
+24V: Printer, solenoid power
+5V: VCC (Logic power)
VDD: Battery charge, Battery back-uped power, CKDC-8 and
RAM Back-up power
4 – 16
Driver
Fig. 9-6
Switching
regulator
F1
+
~
~
-
F2
+5V
Battery
VDD
circuit
Fig. 10-1
LED-display
(for operator)
LED-display
(for custmer)
+24V