Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00

How do I use the SA85 Modbus Plus Card? 

The memory address and station address are set via dip switches on the board.

The device driver 'sa85.sys' must be installed with software interrupt vector at 0x5b (/s5b) and /r2 option. See pages 31-35 of Modicon Plus Network Programming Guide GM-MBPL-002 Rev. A. for more information.

e.g. in config.sys
device=c:\sa85.sys /mc800 /r2 /s5b

Run the TSR 'dos_mp' from winstart.bat before starting up windows.

Boards form
Board name: User supplied unique name
Board type: MBPLUS
Address: 0 Board number as in /n option in 'sa85.sys'. Needed only if more than one board is used
I/O Port: not used
Interrupt: not used
Special Opt: not used
Ports form
Port name: User supplied unique name
Port number: not used
Board name: Use the "Board name" from the Boards form
Baud rate: not used
Data bits: not used
Stop bits: not used
Parity: not used
Special Opt: not used
I/O Devices form
Name: User supplied unique name
Number: Network wide I/O device number
Address: Path to the PLC in the form p.p.p.p.p
e.g. to PLC at node 1:  1
to PLC at node 2 through a bridge at node 5: 5,2
Protocol: MBPLUS
Port name: Use the "Port name" from the Ports form

Note: For maximum performance a virtual port should be created for each Modbus Plus unit. Up to eight ports may be defined per board. Each port can have multiple Modbus Plus units.

Citect.ini option

StringReverse = 0
Do not swab bytes in words of strings.

MsClock = 0
To use the high resolution clock to improve performance set MsClock to 1.

Standard citect.ini options

MaxPending = 2
Block = 238 bytes
Retry = 0
Delay = 0
TimeOut = 2000 milliseconds
PollTime = 20 milliseconds
WatchTime = 30 seconds


  • SA85.SYS - Modbus Plus device driver from MODICON
  • DOS_MP.EXE  - Modbus Plus Driver DOS TSR
  • MBPLUS.DLL - Modbus Plus Driver for windows

Modbus Variables

00001 Output Coils 1 to 99999
10001 Input status 1 to 99999
30001 Input registers 1 to 99999
40001 Output registers 1 to 99999