ProSoft Technology MVI69-MCM - Manual (Page 74)

Ladder Logic MVI69-MCM ♦ CompactLogix or MicroLogix Platform
User Manual Modbus Communication Module
Page 74 of 167 ProSoft Technology, Inc.
March 22, 2011
3.2.4 MODBUS Message Data
This version of the module's program includes formatted pass-through (page
129) mode. In this mode, write messages sent to a slave port are passed directly
through to the processor. It is the responsibility of the ladder logic to process the
message received using this feature. Two data objects are required for this
mode: a variable to hold the length of the message and a buffer to hold the
message. This information is passed from the module to the processor using
block identification codes of 9956 through 9959, depending on the Modbus
function code. Word two of this block contains the length of the message and the
message starts at word 3. Other controller tags are required to store the
controlled values contained in these messages. The MODBUS protocol supports
controller of binary output (coils - functions 5 and 15) and registers (functions 6
and 16).