Investigation Of Transmission Wave Shape/Noise - Mitsubishi Electric PURY-P200 Service Handbook

[3] Investigation of Transmission Wave Shape/Noise

1. M-NET transmission
Control is performed by exchanging signals between outdoor 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
1
❉1 However, minute noise from the DC-DC converter or inverter operation may be picked up.
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
52µs 52µs 52µs 52µs
Logical value Logica valuel
"0" "1"
No fine noise allowed
V = 2.0V or more
HL
V = 1.3V or less
BN
Erroneous operation
No fine noise
allowed
52µs
❉1
- 159 -
Error code
6600
6602
6607
6603
6607
6608
❉1