Circuit Descriptions - Sharp ER-1910 Service Manual

3-3. KDC (4PD7507-036)
The »PD7507-036 is called KDC (Key Display Controller) which is
used to control the keyboard, display, and clock. Communication is
performed with the SC1033C CPU via the 8-bit serial interface.
Fig. 3-2
3-4. Signal description
(0
a
Shift enable
OUT | Reset signal
Key return signal
10 | oS
a eo vispay drive signal hay & scan signal
eS eee ee
te | Fr [OUT | Disa crve signal hey scan signal
OUT ,
Display drive V
Display drive g-
Display drive f
Display drive e
Display drive d
Display drive c
- Display drive b. —
Display drivea
Display drive DP
hm
ER=2395
4. Circuit description
4-1. Oscillation circuit
(1) CPU clock |
| Fig. 4-1
The basic clock is created in the 3MHz crystal oscillator and
connected directly with the CPU. The following SHOWS the waveforms
of signals, X1 and X2.
(2) KDC (Key Display Controller) clock
32.768KH z
®
Clock for timer/calender —
C6 83PF
X2 X1
KDC
"PD 7507C
CL1 —086
ex
Basic clock to UPD7507C ~
Fig. 4-3 ©
From this circuit is delivered the timer, calendar, and «PD7505C
basic clock.
1) Timer and calendar clock
Clock frequency generated across X1 and X2 is adjusted by the
trimmer capacitor (C5) and supplied to the KDC. The trimmer
capacitor has been factory adjusted using the error meter, it
should never be readjusted.
2) »PD7507C basic clock
Clock frequency coming across CL1 and CL2 is adjusted by the ©
potentiometer (VR1) and supplied to the KDC. |
Even. if this. frequency. is observed on the oscilloscope, it. would
not be possible to see an exact waveform because of a
_capacitance. in. the probe. _ .. sega»
_ So, one of the following two methods may 'be used.
[Adjustment-1] | | | O E cates
Observe on the oscilloscope the waveform on the test pin 1 (pin 3)
of the «PD7505C and adjust it. using. VR so that the following
waveform can be seen.
reer 5V
TP 1 | | | |
GND
+-——— 8.8 ~ 9.0ms ——+
Fig. 4-4