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28
10.
TROUBLESHOOTING GUIDE
Problem
Solution
The Master does not receive any
response to its requests.
a) Verify cable polarity A,B.
b) Verify ground connection between Master and Slave.
c) With a long bus cable, check the termination resistors according
with the chapter 4 of this manual.
d) Make sure than the baudrate and the bit settings are the same on
Master and Slaves.
e) Make sure that the Master is including the CRC in the sending,
according with Modbus standard. Check the calculation of CRC.
f) Verify that the function requested is supported by the Slave.
g) Check the Slave address is the one that you are using in the
request. If you are not sure, isolate the Slave (connect it directly to
the Master) and execute a "discovery" process in the Master. In case
that the master has not this kind of process automatically, check
manually the slaves addresses form 1 to 255 with the different
baudrates and bit configurations supported by the Slave.
The Slave does not execute any
request
a) Verify cable polarity A,B.
b) Verify ground connection between Master and Slave.
c) With a long bus cable, check the termination resistors according
with the chapter 4 of this manual.
d) Make sure than the baudrate and the bit settings are the same on
Master and Slaves.
e) Make sure that the Master is including the CRC in the sending,
according with Modbus standard. Check the calculation of CRC.
f) Verify that the function requested is supported by the Slave.
g) Check the Slave address is the one that you are using in the
request. If you are not sure, isolate the Slave (connect it directly to
the Master) and execute a "discovery" process in the Master. In case
that the master has not this kind of process automatically, check
manually the slaves addresses form 1 to 255 with the different
baudrates and bit configurations supported by the Slave.
The Slave does not execute some
requests or the "messages error
rate" is too high.
a) Make sure you are using twisted shielded cable according to
EN50170 (especially with long bus cables or in environments with
high electromagnetic pollution, for example near inverters or
switching power supplies).
b) Verify the cable shielding is connected to ground as in Master as
in Slaves.
c) Check the termination resistors according with the chapter 4 of
Summary of Contents for 57434
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