Reference MVI69E-MBS ♦ CompactLogix Platform
User Manual Modbus Serial Enhanced Communication Module
Page 106 of 154 ProSoft Technology, Inc.
June 28, 2017
7.2.3 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
MVI69E-MBS module.
Read Holding Registers 4x
Multiple Register Write 4x
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.
7.2.4 Read Coil Status (Function Code 01)
Query
This function allows you 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
are 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
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