Function Codes Supported; Exception Responses And Codes - MSA FL500 Operating Manual

1.5.

Function Codes Supported

Function codes 03 and 04 (Read Holding Registers) are used to identify the status of the slave unit. Function
code 06 (Preset Single Register) is used to write a command to the slave unit.
1.6.

Exception Responses and Codes

If a communication error occurs, the FL500 does the following:
 If the FL500 cannot identify the query because of a communication error, or if the FL500 receives the
query, but identifies a communication error, the FL500 does not send back a response. After some time,
the master device goes to a time-out condition for the query.
 If the FL500 receives a query without a communications error, but cannot process the query because of a
Read or Write command to a nonexistent or Illegal Function Code, Data Address (Starting or Register), or
Data Value, the FL500 sends back an exception response.
Byte Modbus Query
1 Slave Address
2 Function Code
3 Exception Code
4 CRC Lo
5 CRC Hi
An exception response includes an exception code in the data field. The exception code describes the
condition that caused the exception.
Code Name
01 Illegal Function
02 Illegal Data Address
03 Illegal Data Value
04 Slave Device Failure An unrecoverable error occurred when the device tried to do a requested
05 Acknowledge
06 Device Busy
Range
1 - 247* (Decimal)
83 or 86 (Hex)
01 - 06 (Hex)
00-FF (Hex)
00-FF (Hex)
Description
The function code received in the query is not applicable.
The data address received in the query is not applicable.
A value contained in the query data field is not applicable.
action.
The request is accepted, but a long period of time is necessary to
process it. This response is given to prevent a time-out error in the
master.
The FL500 is processing a long-duration program command. The master
sends the message again when the slave is free.
FL500 Modbus Communication Operating Manual
FL500 Response
FL500 ID (address)
MSB is set with function code
Applicable exception code
CRC Lo byte
CRC Hi byte
Modbus Interface
7
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