ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 138)

Reference MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 138 of 199 ProSoft Technology, Inc.
June 18, 2014
Master Command List
In order to function in the Master Mode, you must define the module’s Master
Command List. This list contains up to 325 individual entries (for module
firmware versions 3.01 and higher and Add-on-Instruction version 2.8 or higher),
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
 Slave Node Address
 Command Type: Read or Write up to 125 words (16000 bits) per command
 Database Source and Destination Register Address: The addresses where
data will be written or read.
 Count: The number of words to be transferred - 1 to 125 on FC 3, 4, or 16.
Select the number of bits on FC 1, 2, 15.
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. This error list can be
transferred to the processor. The following tables describe the error codes
generated by the module.
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 your device manufacturer for the maximum count
supported by your particular slave.
6.3 Cable Connections
The application ports on the MVI56E-MCM module support RS-232, RS-422, and
RS-485 interfaces. Please inspect the module to ensure that the jumpers are set
correctly to correspond with the type of interface you are using.
Note: When using RS-232 with radio modem applications, some radios or modems require
hardware handshaking (control and monitoring of modem signal lines). Enable this in the
configuration of the module by setting the UseCTS parameter to 1.
6.3.1 Ethernet Cable Specifications
The recommended cable is Category 5 or better. A Category 5 cable has four
twisted pairs of wires, which are color-coded and cannot be swapped. The
module uses only two of the four pairs.
The Ethernet ports on the module are Auto-Sensing. You can use either a
standard Ethernet straight-through cable or a crossover cable when connecting
the module to an Ethernet hub, a 10/100 Base-T Ethernet switch, or directly to a
PC. The module will detect the cable type and use the appropriate pins to send
and receive Ethernet signals.
Ethernet cabling is like U.S. telephone cables, except that it has eight
conductors. Some hubs have one input that can accept either a straight-through
or crossover cable, depending on a switch position. In this case, you must ensure
that the switch position and cable type agree.