Chapter 9 Deployment CPU 21xSER-1 Manual VIPA CPU 21x
9-28 HB103E - Rev. 05/45
The communication by Modbus knows 2 kinds of error:
• Slave doesn't respond to a master command
When the slave is not reacting within the defined timeout period, the
master writes the following error message into the receive block:
ERROR01 NO_DATA. In hex notation the following values are shown:
DB11.DBD 0
DW#16#4552524F
with 45 →
52 →
52 →
4F →
Respond telegram
E
R
R
O
DB11.DBD 4
DW#16#52000120
with 52 →
0001 →
20 →
Respond telegram
R
0001h:1 (as word)
" "
DB11.DBD 8
DW#16#4E4F2044
with 4E →
4F →
20 →
44 →
Respond telegram
N
O
" "
D
DB11.DBD 12
DW#16#41544100
with 41 →
54 →
41 →
00 →
Respond telegram
A
T
A
00h: (Zero scheduling)
• Slave answers with an error message
If the slave replies an error, the function code with 80h is send back
marked with an OR.
DB11.DBD 0
DW#16#05900000
with 05 →
90 →
0000 →
Respond telegram
slave address 05h
function code 90h (error message because
10h OR 80h = 90h)
rest data is irrelevant because an error was
announced
Receive block with
error respond
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