ProSoft Technology MVI71-MCM - Manual (Page 96)

MVI71-MCM ♦ PLC Platform Reference
Modbus Communication Module
Page 96 of 111 ProSoft Technology, Inc.
December 28, 2007
The port configuration error words have the following definitions:
Bit Description Value
0 Type code is not valid. Enter a value from 0 (master) to 1
(slave). 0x0001
1 The float flag parameter is not valid. 0x0002
2 The float start parameter is not valid. 0x0004
3 The float offset parameter is not valid. 0x0008
4 Protocol parameter is not valid. 0x0010
5 Baud rate parameter is not valid. 0x0020
6 Parity parameter is not valid. 0x0040
7 Data bits parameter is not valid. 0x0080
8 Stop bits parameter is not valid. 0x0100
9 Slave ID is not valid. 0x0200
10 Input bit or word, output word and/or holding register
offset(s) are not valid. 0x0400
11 Command count parameter is not valid. 0x0800
12 Spare 0x1000
13 Spare 0x2000
14 Spare 0x4000
15 Spare 0x8000
5.9 Frequently Asked Questions
5.9.1 What is the MVI71-MCM?
The MVI71-MCM is a single slot solution that allows Modbus devices to interface
easily with a PLC processor. The module has 2 ports individually configurable
either as a Modbus Master or Modbus Slave.
The module has an internal database with 5000 registers that are accessible to
external Modbus devices as well as accessible to the PLC through the rack
backplane. Ladder logic is required, among other tasks, to access the MVI71-
MCM internal database.
5.9.2 Why does the module have to break down the data in blocks of
64 words?
Because of a limitation of the PLC backplane that allows only 64 words at a time.
5.9.3 How do I read and write data between the internal MVI71-MCM
database and the PLC?
Ladder logic is required to read and write blocks from the MVI71-MCM. Initially
you must configure the Read and Write Data areas inside the MVI71-MCM
database. It creates 2 regions: the Read Data area which is constantly read from
the module database to the PLC, and the Write Data area which is constantly
written from the PLC ladder logic to the MVI71-MCM database.