Publication 1762-RM001C-EN-P
Protocol Configuration E-11
The controller responds to the Modbus command function codes listed in
Table E.6 below:
Upon receiving a Modbus command that is not supported or improperly
formatted, the controller will respond with one of the exception codes
listed in Table E.7 below:
Table E.6 Supported Modbus Commands
(MicroLogix 1200 Controllers and MicroLogix 1500 1764-LSP Series B and 1764-LRP Processors only)
Command Function Code
(decimal)
Subfunction Code
(decimal)
Read Coil Status 1 -
Read Input Status 2 -
Read Holding Registers 3 -
Read Input Registers 4 -
Set and Reset Single Coil 5 -
Write Single Holding Register 6 -
Echo Command Data 8 0
Clear Diagnostic Counters 8 10
Set and Reset Multiple Coils 15 -
Write Multiple Holding Registers 16 -
Table E.7 Modbus Error Codes
(MicroLogix 1200 Controllers and MicroLogix 1500 1764-LSP Series B and 1764-LRP Processors only)
Error
Code
Error Description Transmitted
Exception Code
(1)
0 No error. none
1 Function Code cannot Broadcast. The function does not support Broadcast. nothing transmitted
2 Function Code not supported. The controller does not support this Modbus function or
subfunction.
1
3 Bad Command Length. The Modbus Command is the wrong size. 3
4 Bad Length. The function attempted to read/write past the end of a data file. 3
5 Bad parameter The function cannot be executed with these parameters. 1
6 Bad File Type The file number being referenced is not the proper file type. 2
7 Bad File Number The file number does not exist 2
8 Bad Modbus Address
The function attempted to access an invalid Modbus address.
(2)
3
9 Table Write protected The function attempted to write to a read-only file. 3
10 File Access Denied Access to this file is not granted. 2
11 File Already Owned Data file is already owned by another process, 2
(1) If Modbus Command is sent with a valid Broadcast address, then no exception reply will be sent for Error Codes 2 through 11.
(2) See Table E.4 on pageE-9 for valid Modbus memory mapping.
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