ProSoft MVI69E-MBS User Manual page 73

MVI69E-MBS ♦ CompactLogix Platform
Modbus Serial Enhanced Communication Module
Important: Take care when constructing each command in the list to ensure predictable operation
of the module. If two commands write to the same internal database address of the module, the
results are invalid. All commands containing invalid data are ignored by the module.
Master Command List
For a port to function in Master Mode, its Master Command List must be defined
in Prosoft Configuration Builder; refer to Modbus Port x Commands (page 52).
This list contains up to 310 individual entries, with each entry containing the
information required to construct a valid command. A valid command includes
the following items:

Command enable mode: (0) disabled, (1) continuous or (2) conditional

Source or destination database address: The module database address
where data is written or read.

Count: The number of words or bits to be transferred – up to 125 words for
Function Codes 3, 4, or 16, and up to 2000 bits for Function Codes 1, 2, or
15.
Note: 125 words is the maximum count allowed by the Modbus protocol. Some field devices may
support less than the full 125 words. Check with the device manufacturer for the maximum count
supported by the particular slave device.

Slave node address

Modbus Function Code: This is the type of command that is issued.

Source or destination address in the slave device
Command Error Codes
As the list is read in from the processor and as the commands are processed, an
error value is maintained in the module for each command. The definition for
these command error codes is listed in Communication Error Codes (page 100).
You can view the command error codes through the Ethernet diagnostics port;
refer to Diagnostics and Troubleshooting (page 87). They can also be transferred
from the module's database to the processor.
To transfer the Command Error List to the processor, set the Command Error
Offset parameter in the port configuration to a module database address that is in
the module's Read Data area; refer to Additional Configuration Parameters as
Master (page 50).
Note: The Command Error List must be placed in the Read Data area of the database, so it can be
transferred to the processor in the input image.
ProSoft Technology, Inc.
June 28, 2017
MVI69E-MBS Backplane Data Exchange
Page 73 of 154
User Manual