Hitachi RAM-68NP3B, Service Manual, Page: 53 / 79

●
One (IC32) 8-bit type shift register ICs that convert serial signal input to parallel and output the parallel
signals are used on the circuits of electric expansion valves 3.
●
An example of circuit operation when an expansion valve is powered is shown in the time chart in Fig. 5-3.
①
A clock signal (16 cycles at 750µs/cycle) is output from pin
㉒
on the microcomputer.
(One cycle for the clock signal is 500µs off, 250µs on.)
②
A serial signal
＃
1
of the power pattern is synced with the clock signal and output from pin
㉔
of the microcomputer.
＃
1 The serial signal is the pattern of the current applied to phase 1 or phase 2 of a 4-phase wound wire on
an expansion valve, that has then been converted to serial format. A serial signal is output so that the
center of the ON serial signal (Hi-level 500µs) aligns with the rising edge of the clock signal.
The content of the shift register in IC is updated by operations
①
and
②
described above.
Next, 250µs after the ON signal is output for the 16th cycle of the clock signal,
③
the latch signal from pin
㉓
on the microcomputer is turned OFF (Lo-level 500µs) and then ON again (Hi-level).
④
After the time required to apply current has elapsed, if powering of the expansion valve is required the cycle
returns to
①
and repeats the operation.
With the operation described above, the opening of expansion valves is controlled while applying current to phase 1
or phase 2 of a 4-phase wound wire on an expansion valve, according to the content of the shift register updated
when the current is applied. When the opening of the expansion valve reaches the target amount, the stop pattern
described in
②
above is applied and then operations
①
-
④
are performed to complete the control of the
expansion valve.
0V
0V
0V
0V
0V
0V
0V
0V
0V
Fig. 5-3 Time Chart
250µs 250µs
500µs
500µs 500µs
Current application time 25ms Current application time 500ms or 25ms
Stop pattern, 13ms Power pattern, last 13ms
⑯
Electric Expansion Valve 3
④
⑮
Electric Expansion Valve 3
③
⑭
Electric Expansion Valve 3
②
⑬
Electric Expansion Valve 3
①
IC34
Serial signal
IC32
Latch signal
0V
Clock signal
IC32
㉔
Pin serial signal
㉓
Pin latch signal
㉒
Pin clock signal Microcomputer