With the RS 422 ports configured as standard SYMAX ports, the MEB module performs a SYMAX to Modbus Plus protocol translation. It is therefore possible to have two SYMAX processors communicating via Modbus Plus, provided each SYMAX processor is connected to a MEB module. A Citect system, installed with a SA85 card interface card can be connected via Modbus Plus to a SYMAX PLC by utilising a MEB.

MEB Address Configuration:

Using the MEB software, configure the RS422 ports on the MEB module with valid SY/NET addresses e.g. Yxx, where Y = 0 or 1 and xx = 00 to 99. Configure the Modbus Plus port on the MEB to a valid Modbus address e.g. zz, where zz = 00 to 64. Ensure the Modbus and RS422 ports do not have the same address e.g. 010 and 10 conflict.

SYMAX PLC to SYMAX PLC via Modbus Plus:

To communicate using TWRITE or TREAD instructions, use the following address routing:

[RS422 Source], [Modbus Source], [Modbus Destination], [RS422 Destination Path]

where RS422 Destination Path:
= 1 if SYMAX processor is connected to RS422 MEB port 1
= 2 if SYMAX processor is connected to RS422 MEB port 2

CITECT to SYMAX PLC via Modbus Plus:

Install the SA85 card in the Citect PC. Include the device driver in the autoexec.bat file. Ensure the device driver is configured with the /r2 and /s5B options. Refer to Citect Design Guide and Q1683 for further information.

In your Citect communications configuration, specify the following:

Boards:
Board Name - Board Name
Board Type - MBPLUS
Address - 0

Ports:
Port Name - Port Name
Board Name - Board Name

IO Devices:
Protocol - MBPLUS
Port Name - Port Name
Address -  [Modbus Destination], [RS422 Destination Path]

where RS422 Destination Path:
= 1 if SYMAX processor is connected to RS422 MEB port 1
= 2 if SYMAX processor is connected to RS422 MEB port 2