ProSoft Technology MVI56E-MNET/MNETXT User Manual
Page 126
Reference
MVI56E-MNET / MNETXT ♦ ControlLogix Platform
User Manual
Modbus TCP/IP Interface Module
Page 126 of 181
ProSoft Technology, Inc.
April 23, 2014
Pass-Through Blocks (9956-9961, 9970 and 9996)
In Pass-Through mode, write messages sent to a server port are passed directly
through to the processor. In this mode, the module sends special blocks to the
processor when a write request is received from a Client. Ladder logic must
handle the receipt of these blocks and place the enclosed data into the proper
controller tags in the processor.
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
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
5
9959
15
9960
22
9961
23
9970
99
Pass-Through Blocks 9956, 9957, 9958, 9960 or 9961 from Module to Processor
Word Offset
Description
Length
0
0
1
1
9956, 9957, 9958, 9960 or 9961
1
2
Number of word registers in Modbus data set
1
3
Starting address for Modbus data set
1
4 to 248
Modbus data set
245
249
9956, 9957, 9958, 9960 or 9961
1