Investigation Of Transmission Wave Shape/Noise - Mitsubishi Electric City Multi PQHY-P72 Service Handbook

[3] Investigation of Transmission Wave Shape/Noise

1. M-NET transmission
Control is performed by exchanging signals between the heat source unit and the indoor unit (M-NET remote controller)
through M-NET transmission. Noise interference on the transmission line will interrupt the normal transmission, leading to
erroneous operation.
(1) Symptoms caused by noise interference on the transmission line
Cause
Noise interference on
the transmission line
(2) Wave shape check
[With transmission]
[Without transmission]
Check the wave pattern of the transmission line with an oscilloscope. The following conditions must be met.
1) Small wave pattern (noise) must not exist on the transmission signal. Minute noise (approximately 1V) can be gen-
erated by DC-DC converter or the inverter operation; however, such noise is not a problem when the shield of the
transmission line is grounded.
2) The sectional voltage level of transmission signal should be as follows.
Logic Voltage level of the transmission line
0
1
Erroneous operation
Signal is transformed and will be misjudged as the
signal of another address.
Transmission wave pattern is transformed due to
the noise creating a new signal
Transmission wave pattern is transformed due to
the noise, and will not be received normally leading
to no acknowledgement (ACK).
Transmission cannot be performed due to the fine
noise.
Transmission is successful; however, the acknowl-
edgement (ACK) or the response cannot be re-
ceived normally due to the noise.
V
HL
V
BN
52 52 52
Logic "0" Logic "1"
V = 2.0V or higher
HL
V = 1.3V or below
BN
- 265 -
Error code
No fine noise
allowed
52 52
No fine noise allowed
[ IX Troubleshooting ]
Error code definition
6600 Address overlaps
6602 Transmission pro-
cessor hardware er-
ror
6607 No ACK
6603 Transmission circuit
bus-busy
6607 No ACK
6608 No response