Mitsubishi Electric PQRY-P200YEM-A Service Handbook page 86

(8) Investigation of transmission wave shape/noise
Control is performed by exchanging signals between heat source unit, indoor unit and remote controller by M-NET
transmission. If noise should enter into the transmission line, the normal transmission will be hindered causing
erroneous operation.
1) Symptom caused by the noise entered into transmission line
Cause
Noise entered into
transmission line
2) Method to confirm wave shape
<With transmission>
<Without transmission>
Check the wave shape of transmission line with an oscilloscope to confirm that the following conditions are being
satisfied.
1 The figure should be 104µs/bit ± 1%.
2 No finer wave shape (noise) than the transmission signal (52µs ± 1%) should be allowed. 1
3 The sectional voltage level of transmission signal should be as follows.
Logic value Transmission line voltage level
0 V
HL
1 V
BN
1 However, minute noise from the DC-DC converter or inverter operation may be picked up.
Erroneous operation
Signal changes and is misjudged as the signal of other
address.
Transmission wave shape changes to other signal due to
noise.
Transmission wave shape changes due to noise, and can
not be received normally thus providing no reply (ACK).
Transmission can not be made continuously due to the
entry of fine noise.
Transmission can be made normally, but reply (ACK) or
answer can not be issued normally due to noise.
V
HL
V
BN
52 µs 52 µs 52 µs
Logical value "0" Logical
= 2.0V or more
= 1.3V or less
No fine noise allowed
52 µs 52 µs
value "1"
No fine noise allowed 1
–85–
Error code
6600
6602
6607
6603
6607
6608
1