Applies To:
  • CitectSCADA

A combination of COM1: and ASCII_DEV are used in the devices form. This is done so as to use a serial printer and bypass the Windows Printer Manager, in order that one line can be printed at a time. It has found that problems due to high Citect CPU usage (as seen in Page General) occur. For example, extremely slow page update rates. 

This combination is not currently supported by Citect. COM1: and LPT1: are normally used with PRINTER_DEV so that outputs are managed through the Windows Printer Manager. Citect does not spool output to COM1: or LPT1:, so unless used with PRINTER_DEV for printouts, high CPU usage problems can result.

However the combination of LPT1.DOS and ASCII_DEV is supported as described in Knowledge Base article Q1113. In this case, spooling is done by Citect in a separate thread and no high CPU usage problems should result.

Currently the combinations COM1: and ASCII_DEV, COM1.DOS and ASCII_DEV, LPT1: and ASCII_DEV may result in problems due to high CPU usage and are not recommended to be used.

A spooling device, type 5, can be used to spool ASCII data from the com port to another terminal.  For example sending Alarm data to a Unix host, via a Comport/Terminal server could use a Device set up as per;

Name:         Terminal

Format:        {TIME,11} {TAG,16} {NAME,32}{STATE,9}{COMMENT,2}

File Name:    COM1.DOS

Type:            5

No. Files:    -1

This would be useful to keep cpu usage low and will be unaffected if the host link is down.