Applies To:
  • CitectSCADA
Summary:
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. 

Solution:
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.

 
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