10
DEDICATED INSTRUCTIONS
10.3 Z(P).MBREQ
10 - 22
9
PROGRAMMING
10
DEDICATED
INSTRUCTIONS
11
TROUBLESHOOTINGAPPENDICESINDEX
POINT
1. In the case of the MBREQ instruction, exception codes and function codes
are not stored in the Error log (address: 0CFE
H to 0DFFH) of the buffer
memory.
Check the exception and function codes by the response message that is
stored in the response message storage device.( This section (4))
2. This instruction completes normally even if the target slave device returns an
exception response.
When the instruction completes normally, check the most significant bit of the
function code in the response message to determine whether the response is
normal or not. (For an error response, the most significant bit in the first byte
of the receive data turns ON.)
In the case of an error response, check the exception code (the second byte
of the receive data) in the response message and take corrective
actions.( Section 11.4.2)
3. For the MBREQ instruction, the ACK. and NAK states of the detailed LED
status do not change.
Check whether communication processing completes normally or not by the
response message stored in the response message storage device. (
This section (4))
4. Pay attention to the following when sending a request message to a slave
with no response message
*1
expected. (Excluding the case of broadcast)
• Specify sufficient time in the Response monitoring timer value (S1)+7 for
the slave to process the request message.
• A response monitoring timeout error (error code: 7379
H) occurs even if
the instruction is completed normally.
Regard the response monitoring timer timeout error (error code: 7379
H)
as normal completion.
* 1 Request messages for which no response message is returned are as follows. (in the case of
MODBUS standard function)
Switching to the Listen only mode ( Section 4.11.5)
Restart communications option sent to a slave in the Listen only mode
( Section 4.11.2)
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