ProSoft Technology MVI56E-MNETR - Manual (Page 121)

Reference MVI56E-MNETR ♦ ControlLogix Platform
User Manual Modbus TCP/IP Interface Module with Reduced Data Block
ProSoft Technology, Inc.
Page 121 of 153
August 31, 2009
5.5 Modbus Protocol Specification
The following pages give additional reference information regarding the Modbus
protocol commands supported by the MVI56E-MNETR.
5.5.1 Commands 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 functions supported by the module.
Function Code Definition Supported in Client Supported in Server
1 Read Coil Status X X
2 Read Input Status X X
3 Read Holding Registers X X
4 Read Input Registers X X
5 Set Single Coil X X
6 Single Register Write X X
7 Read Exception Status X
8 Diagnostics X
15 Multiple Coil Write X X
16 Multiple Register Write X 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 TCP/IP
Server device.
5.5.2 Read Coil Status (Function Code 01)
Query
This function allows the user to obtain the ON/OFF status of logic coils used to
control discrete outputs from the addressed Server only. Broadcast mode is not
supported with this function code. In addition to the Server 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 will be
interrogated to obtain status data.
The addressing allows up to 2000 coils to be obtained at each request; however,
the specific Server 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 from Server device number 11.
Adr Func Data Start Pt Hi Data Start Pt Lo Data # Of Pts Ho Data # Of Pts Lo Error Check Field
11 01 00 13 00 25 CRC