Siemens SICAM Q100 System Manual page 91

Notes for Commissioning
If a Modbus slave device is connected correctly, the serial parameters (baud rate and parity) are identical to the
parameterization in the Modbus master of SICAM Q100, the device address was checked, and the errors "no
responses" and/or "CRC errors" still occur (sporadically), proceed as follows:
• Try to increase the Response timeouts. Some devices may take longer to respond (in particular when
reading a larger number of values with one message) or at low baud rates.
• Try to increase the Additional inter-character timeout. There may be larger message gaps during the
transmission or a device needs a longer bus silent interval.
Check the correct design of the RS485 bus line, that is, the line topology with terminating resistors at both ends,
fail-safe resistors if necessary at least at one end (see chapter 13.1.3 in the device manual). Stubs (that is,
longer single feeders from the bus line to devices) must be avoided.
Last Modbus TCP/RTU Gateway Messages
Available only if the Modbus gateway function is activated.
• Status:
• Name:
• Dev.addr.:
• Fct.code:
• Start addr.:
• Qty. of regs:
• Last request:
• Client IP:Port:
SICAM Q100, 7KG95xx, System Manual
E50417-C1040-C522-A8, Edition 09.2020
Status of the request messages

Good: correct response

No response: the bus device does not respond (for example, communication
failure)

Exception responses (n): exception response sent with error code

CRC error: a CRC error was detected in the response
Name of the Modbus slave device to which the request message was sent. The
name is only available if the Modbus slave device was also parameterized in
the Modbus RTU Master (active parameter set). Otherwise, "-" is entered.
Device address of the Modbus slave device to which the request message be-
longs.
Modbus function code used in the request message.
Start register address when reading data of this request message.
Number of registers requested in this message.
This value indicates how many ms ago the data were requested. It is a snap-
shot referring to the last update of the diagnostic page in the user interface. It
cannot be used to determine the sending time exactly.
IP address and TCP port number of the Modbus TCP client that sent the re-
quest.
Communication
2.3 Modbus RTU Master
91