Hitachi RAM-68NP3B, Service Manual, Page: 57 / 79

8. Indoor/outdoor communication circuit
<Typical communication waveform>
Microcomputer
transmission signal
Microcomputer
reception signal
Signal between connecting
cable 2 and 3
<Enlarged waveform>
Fig. 5-2
Fig. 5-1
Indoor side
c
b
a
d
e
a
Signal sent by indoor microcomputer
５mS／DIV
1V
／
DI
V
0V
d
Signal sent by outdoor microcomputer
５mS／DIV
1V
／
DI
V
0V
30kHz demodulated waveform
e b
Signal sent by indoor and outdoor
microcomputer
５mS／DIV
1V
／
DI
V
0V
c Signal between connecting cable 2 and 3
５mS／DIV
1V
／
DI
V
0V
30kHz demodulated waveform
The unit is receiving a signal that it sent
(It is not used particularly as a signal)
c
c
a
b
Outdoor reception
circuit for Indoor 1
Main
microcomputer
Outdoor switching 1
Outdoor main
circuit
Outdoor side Indoor side
B-0V
R015
R861
C862
C863
R864
F10
C864
R866
R862
1
2
3
1
L
N
2
3
1
2
3
1
2
3
Q825
L805
R863
B-15V
40
57 56 38 37
39
B-0V
R014
R851 C852 C853
R854 C854
R856
R852
Q824
L804
R853
B-15V
d
e
d
e
27
28
F9
Indoor side
transmission circuit
Indoor side reception circuit
The communication
chopper output out
of room (30kHz)
Indoor
Transmision
Output
Indoor
Reception
Input
Indoor
Microcomputer (IC601)
Ｃ
343
Ｒ
341
Ｃ
342
Ｃ
302
Ｒ
309
Ｒ342
Ｒ
310
Ｒ
311
Ｒ331
Ｒ332
Ｑ332
Ｃ341
Ｔ301
0Ｖ
12Ｖ
0Ｖ
Ｑ331
88
52
51
Outdoor transmitting
circuit for Indoor 1
Approx.
450µs
Approx.
750µs
Microcomputer
transmission signal
Microcomputer
reception signal
Outdoor side
Outdoor unit
reception
input 1
Outdoor unit
transmission
output 1
Outdoor unit
reception
input 2
Outdoor unit
transmission
output 2
Communication switching circuit
Outdoor switching 2
Outdoor switching 3
Outdoor switching 4
Outdoor reception
circuit for Indoor 2
Outdoor transmitting
circuit for Indoor 2
c
1
2
3
1
2
3 R013
R841 C842 C843
R844 C844
R846
R842
L803
R843
B-15V
F8
B-0V
Q823
Outdoor reception
circuit for Indoor 3
Outdoor transmitting
circuit for Indoor 3
*
*
Check
If the communication fails between the indoor and outdoor units for some reason, the product will give a self-diagnosis
display either by “the timer lamp blinking 3 times (indoor failure)” or “the the timer lamp blinking 12 times (outdoor failure)”
depending on the cause.
Indoor and outdoor communications are conducted by using lines 2 and 3 of connecting cable. Line 2 of connecting cable is share
with a transmission channel that powers the indoor unit.
Data communicated between the indoor and outdoor units are outputted from the microcomputer as serial signals and are
transmitted as demodulated by a 31kHz carier wave (for indoor) and a 30kHz carier wave (for outdoor).