Mitsubishi Electric HP120TNU-A Service Handbook page 258

[8-4 Checking Transmission Waveform and for Electrical Noise Interference ]
8-4-2 MA Remote Controller
The communication between the MA remote controller and the indoor unit is performed with current tone burst.
(1) Symptoms caused by noise interference on the transmission line
If noise is generated on the transmission line, and the communication between the MA remote controller and the indoor unit
is interrupted for 3 minutes in a row, MA transmission error (6831) will occur.
(2) Confirmation of transmission specifications and wave pattern
MA remote controller
Transmission waveform (Across terminal No.1 - 2)
Logic 1
12msec
HWE18220_GB
TB15
A
B
Indoor unit
Logic 0 Logic 1 Logic 1
12msec 12msec 12msec
1
A, B : No polarity
2
Across terminal No. 1-2
: Power supply (9V to 12VDC)
Satisfies the formula
12 msec/bit
DC9~12V
Voltage among terminals must
be between DC9 and 12 V.
5%
17
chapter 8 -