M-Net Transmission Waveform And Noise Check Procedure - Mitsubishi Electric AE-200A Service Handbook

[V Troubleshooting]

[4] M-NET transmission waveform and noise check procedure

The AE-200/AE-50/EW-50 performs control while signals are exchanged between AE-200/AE-50/EW-50, outdoor units, indoor units,
and remote controllers (M-NET remote controllers) through M-NET. The interference of noise or the like on the transmission line will
cause normal transmission to no longer be possible and erroneous operation.
(1) Symptoms caused by the interference of noise on the transmission line
Cause
The signal is transformed and is mistaken as a signal
from a different address.
The sent waveform is transformed to a different signal
due to noise.
Interference of noise The sent waveform is transformed due to noise and
on the transmission the other party cannot receive the signal normally
line leading to no acknowledgment (ACK).
The state of being unable to send continues due to
small noise interference.
Sending is successful but the acknowledgment (ACK)
or the response is not returned normally due to noise.
(2) Waveform check procedure
[With transmission]
[Without transmission]
Waveform check procedure
Check the waveform of the transmission line with an oscilloscope. The following conditions must be met.
1) There must be no small waveform (noise) in the transmission signal.
(Small noise of approximately 1 V caused by the operation of a DC-DC converter or inverter may be noticeable but such
noise should not be a problem when the unit and transmission line shield are grounded.)
2) The voltage level of each portion of the transmission signal must be as follows.
Logic
[Supplementary explanation] Oscilloscope settings
・ Band with 300 MHz or higher
・ V/div: 2 V/div AC coupling
・ T/div: 20 to 100 μsec/div
Malfunction
V
EFF
V
EFF
Transmission line effective voltage
level
0
17 V ≤ V
EFF
1
Error code
6600
6602
6607
6603
6607
6608
Transmission line signal voltage
VHL = 2.5 V or higher
≤ 32 V
VBN = 1.3 V or lower
69
Error description
Communication error - Address
duplicate
Communication error -
Transmission processor hardware
error
Communication error - No ACK
return
Communication error -
Transmission line busy
Communication error - No ACK
return/No return of response
frame
level