Modbus Protocol Specification; Read Coil Status (Function Code 01) - ProSoft Technology inRAX MVI56E-MNETCR User Manual

Reference
User Manual
5.5

Modbus Protocol Specification

The following pages give additional reference information regarding the Modbus
protocol commands supported by the MVI56E-MNETCR.

5.5.1 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
11 01 00
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Modbus TCP/IP Multi Client Enhanced Communications Module for Remote Chassis
Data Start Pt Lo Data # Of Pts Ho Data # Of Pts Lo
13 00
MVI56E-MNETCR ♦ ControlLogix Platform
Error Check Field
25 CRC
ProSoft Technology, Inc.
June 14, 2011