Applies To:
  • CitectSCADA 5.xx, 6.00

Users have found that when they have a transient condition resulting in a failed dialup attempt with dialup I/O, Citect SCADA will not use that modem again.

The problem occurs when you have modems in the modem pool that have different requirements (Example: different data frame or rate). The scenario in particular is that if all modems supporting one type of requirement have had error conditions (line busy, no answer, etc) then they will not be released for reuse until all modems regardless of their configuration have failed. The system will look constantly for a compatible modem and none will be found so will just wait. This waiting will continue until all modems in the entire pool have failed resetting all the modems for retry. In general, most customers have all identically configured modems so this issue never arises. 

Citect has confirmed this to be a problem in CitectHMI/SCADA versions 5.XX to 6.00. This problem has been fixed in version 6.00A and above by treating each configuration combination as a separate group and resetting modems of same configuration once they have all been marked unusable.

dialup modem schedule incompatible unusable