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Checking Transmission Waveform And For Electrical Noise Interference; M-Net - Mitsubishi Electric PURY-HP72 Service Handbook

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[8-4 Checking Transmission Waveform and for Electrical Noise Interference ]

8-4
Checking Transmission Waveform and for Electrical Noise
Interference
8-4-1

M-NET

Control is performed by exchanging signals between the outdoor unit and the indoor unit (ME remote controller) through M-
NET transmission. Noise interference on the transmission line will interrupt the normal transmission, leading to erroneous op-
eration.
(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]
Wave shape check
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 generated 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
0
1
HWE13080
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
Logic "0"
Voltage level of the transmission line
V
= 2.5V or higher
HL
V
= 1.3V or below
BN
Error code
No fine noise
allowed
52
52
52
Logic "1"
No fine noise allowed
- 264 -
Error code definition
6600
Address overlap
6602
Transmission pro-
cessor hardware er-
ror
6607
No ACK error
6603
Transmission line
bus busy error
6607
No ACK error
6608
No response error
GB

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