ProSoft Technology MVI69L-MBS - Manual (Page 107)

MVI69L-MBS ♦ CompactLogix Platform Reference
Communication Module User Manual
ProSoft Technology, Inc. Page 107 of 154
January 6, 2014
7.2.1 Function Codes Supported by the Module
The format of each command in the list depends on the Modbus Function Code
being executed.
The following table lists the Function Codes supported by the module.
Function Code Definition Supported as Master Supported as Slave
1 Read Coil Status 0x X X
2 Read Input Status 1x X X
3 Read Holding Registers 4x X X
4 Read Input Registers 3x X X
5 Set Single Coil 0x X X
6 Single Register Write 4x X X
8 Diagnostics X
15 Multiple Coil Write 0x X X
16 Multiple Register Write 4x X X
17 Report Slave ID X
22 Mask Write 4X X
23 Read/Write X
Each command list record has the same general format. The first part of the
record contains the information relating to the communication module and the
second part contains information required to interface to the Modbus slave
device.
7.2.2 Read Coil Status (Function Code 01)
Query
This function allows the user to obtain the ON/OFF status of logic coils (Modbus
0x range) used to control discrete outputs from the addressed Slave only.
Broadcast mode is not supported with this function code. In addition to the Slave
address and function fields, the message requires that the information field
contain the initial coil address to be read (Starting Address) and the number of
locations that is interrogated to obtain status data.
The addressing allows up to 2000 coils to be obtained at each request; however,
the specific Slave device may have restrictions that lower the maximum quantity.
The coils are numbered from zero; (coil number 1 = zero, coil number 2 = one,
coil number 3 = two, and so on).
The following table is a sample read output status request to read coils 0020 to
0056 (37 coils) from Slave device number 11.
Note: This is the structure of the message being sent out to the Modbus network. The byte values
below are in hexadecimal display