ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 122)

Reference MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 122 of 199 ProSoft Technology, Inc.
June 18, 2014
6.2.4 Special Function Blocks
Special function blocks are optional blocks used to control the module or request
special data from the module. The current version of the software supports the
following special function blocks:
 Event Command
 Slave Status
 Command Control
 Module Configuration
 Master Command Data List
 Pass-Through
 Warm Boot
 Cold Boot
 Write Configuration
Event Command Blocks (1000 to 1255 or 2000 to 2255)
Event Command blocks send Modbus commands directly from the ladder logic to
one of the Master Ports. The following table describes the format for these
blocks.
Block Request from Processor to Module
Word Offset Description Length
0 1000 to 1255 or 2000 to 2255 1
1 Internal DB Address 1
2 Point Count 1
3 Swap Code 1
4 Modbus Function Code 1
5 Device Database Address 1
6 to 247 Spare 242
The block number defines the Modbus Port that will send the command, and the
Slave node that will respond to the command. Blocks in the 1000 range are
directed to Modbus Port 1, and blocks in the 2000 range are directed to Modbus
Port 2. The Slave address is represented in the block number in the range of 0 to
255. The sum of these two values determines the block number. The other
parameters passed with the block are used to construct the command.
 The Internal DB Address
parameter specifies the module’s database
location to associate with the command
 The Point Count parameter defines the number of points or registers for the
command
 The Swap Code is used with Modbus function 3 requests to change the word
or byte order
 The Modbus Function Code has one of the following values 1, 2, 3, 4, 5, 6,
15, or 16
 The Device Database Address is the Modbus register or point in the remote
Slave device to be associated with the command