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

This is a description of the COMx serial port driver. 

This driver use the Windows COM port driver to access the COM serial ports.
Boards form
Board name: User supplied unique name for the board.
Board type: COMx
Address: The number of the port - starting from 1.
I/O Port: not used
Interrupt: not used
Special Opt: not used
Ports form
Port name: User supplied unique name for the port.
Port number not used
Board name: Use the Board name from the Boards form.
Baud rate: up to 57600 may be used
Data bits: 7 or 8
Stop bits: 1 or 2
Parity: 0, 1 or 2 (for none, odd and even parity)
Special Opt: -h Use DTR (data-terminal-ready) and RTS (request-to-send) signal for reception flow control, monitor CTS (clear-to-send) and DSR (data-set-ready) signal for output flow control.
-r Raise DTR only when transmitting.
-t Raise RTS only when transmitting.
-i String Dial modem string. This string is sent whenever the port is initialised. Special characters are
'~' delay for 500 milliseconds
'~{60}' delay for 30 (500*60) seconds.
'\M' send carriage return

Citect.ini options:

PollMode = 0
Use the 20 milliseconds timer to generate psuedo receive and transmit interrupts. If PollMode is set to 1, then [protocol]PollTime must be non zero.

TimerResolution = 20 milliseconds
Set the timer resolution to 20 milliseconds. Settting this value to a lower value will increase CPU usage. The 55 milliseconds timer will be used if TimerResolution and PollMode are both 0.

TxReset = 1
Reset COM port before each transmission of a frame of characters, if -r or -t options is used. This is done to fix a bug in the Windows driver.


COMX.DLL COMX Driver for windows


  • Transmit buffer size 600 bytes
  • Receive buffer size 1600 bytes
  • Maximum number of ports 9

Initialisation errors (in Hexadecimal):

ffff Invalid or unsupported port number or baudrate
fff6 Hardware not present
fff4 Unsupported baudrate