MVI56E-MNETR ♦ ControlLogix Platform
Reference
Modbus TCP/IP Interface Module with Reduced Data Block
User Manual
ProSoft Technology, Inc.
Page 123 of 175
June 14, 2011
The ladder logic should copy and parse the received message and control the
processor as expected by the master device. The processor must respond to the
pass-through control block with a write block. The following table describes the
format of the write block.
Unformatted Pass-Through Command (Write Block)
Offset
Description
Length
0
9996
1
1 to 41
Spare
41
This informs the module that the command has been processed and can be
cleared from the pass-through queue.
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 received by the module. 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 9956 passes word type data
for functions 6 and 16. Block 9957 passes a floating-point message for functions
6 and 16. Block 9958 is utilized when Modbus function 5 data is received. Block
9959 is employed when function 15 is recognized. Block 9960 is used for
function 22 and Block 9961 is used for function 23 requests. Block 9970 is
utilized for function 99. The following tables describe the format for the read
blocks.
Formatted
Formatted Pass-Through Command Blocks (Read Block)
Offset
Description
Length
0
9956, 9957, 9958, 9960 or 9961
1
1
Number of word registers in Modbus data set
1
2
Starting address for Modbus data set
1
3 to 40
Modbus data set
38
41
9956, 9957, 9958, 9960 or 9961
1
