Connection to a fieldbus
6.4 Communication via RS485
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
153
Logical error
If the slave detects a logical error within a request, it responds to the master with an
"exception response". In the response, the highest bit in the function code is set to 1. If the
slave receives, for example, an unsupported function code from the master, the slave
responds with an "exception response" with code 01 (Illegal function code).
Table 6- 35 Overview of exception codes
Exception
code
Modbus name Remark
01 Illegal function code An unknown (not supported) function code was sent to the
slave.
02 Illegal Data Address An invalid address was requested.
03 Illegal data value An invalid data value was detected.
04 Server failure Slave has terminated during processing.
Maximum processing time, p2024[0]
For error-free communication, the slave response time (time within which the Modbus master
expects a response to a request) must have the same value in the master and the slave
(p2024[0] in the inverter).
Process data monitoring time (setpoint timeout), p2040
The alarm "Setpoint timeout" (F1910) is issued by the Modbus if p2040 is set to a value > 0
ms and no process data are requested within this time period.
The alarm "Setpoint timeout" only applies for access to process data (40100, 40101, 40110,
40111). The alarm "Setpoint timeout" is not generated for parameter data (40200 … 40522).
Note
This time must be adapted depending on the number of slaves and the baud rate set for the
bus (factory setting = 100 ms).
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