ABB IRB 6400R Product On-Line Manual page 342

Troubleshooting Tools
RS 422
TXD4/TXD4 N
RXD4/RXD4 N
DATA4/DATA4 N
DCLK4/DCLK4 N
N.B! Only full duplex is supported.
5 V
5 V
Figure 3 Signal description for RS 422, differential transmission.
When measuring the differential RS 422 signals, the oscilloscope should be set for AC
testing. The data transmission has the same structure as RS 232, i.e. 1 start bit + 8 data
bits + 1 stop bit, but the signals are differential. By looking at the "true" channel, it is
possible to read the data.
If the types of signal as shown in the above diagram are obtained when measuring, this
means that the drive circuits and lines are OK. If one or both of the signals do not move,
it is likely that one or several line(s) or one or several drive circuit(s) is/are faulty.
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Signal Explanation
Transmit Data in Full Duplex Mode
Receive Data in Full Duplex Mode
Data Signals in Half Duplex Mode
Data Transmission Clock
Signal XXX
Signal XXX N
f= 9600 38400 baud
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