ProSoft Technology MVI56E-MNETC User Manual

Page 132

Guide to the MVI56E-MNETC User Manual

MVI56E-MNETC ♦ ControlLogix Platform

User Manual

Modbus TCP/IP Client Enhanced Communication Module

Page 132 of 183

ProSoft Technology, Inc.

February 3, 2013

There are two basic modes of operation when the pass-through feature is
utilized: Unformatted (code 1) and Formatted (code 2 or 3). In the unformatted
mode, messages received on the server are passed directly to the processor
without any processing. These unformatted blocks require more decoding than
the formatted blocks.

The Modbus protocol supports control of binary output (coils - functions 5 and 15)
and registers (functions 6 and 16).

Any Modbus function 5, 6, 15 or 16 commands will be passed from the server to
the processor using the block identification numbers 9956 to 9961, 9970 and
9996.

Formatted Pass-Through Blocks (9956 to 9961, 9970)
In formatted pass-through mode, the module processes the received write
request and generates a special block dependent on the function received. There
are two modes of operation when the formatted pass-through mode is selected. If
code 2 is utilized (no swap), the data received in the message is presented in the
order expected by the processor. If code 3 is utilized (swap mode), the bytes in
the data area of the message will be swapped. This selection is applied to all
received write requests. The block identification code used with the request
depends on the Modbus function requested.

Block ID

Modbus Function

9956

6, 16 (word type data)

9957

6, 16 (floating-point)

9958

9959

9960

9961

9970

Pass-Through Blocks 9956, 9957, 9958, 9960 or 9961 from Module to Processor

Word Offset

Description

Length

9956, 9957, 9958, 9960 or 9961

Number of word registers in Modbus data set

Starting address for Modbus data set

4 to 248

Modbus data set

245

249