Why in a M580 HotStandby system, does the system %S21 never move to 1?
When customer uses system bit %S21 in the coding of application, it looks like the bit never move to 1 folowing cold start.
In M580 Hotstandby system each CPU is starting all the time in “Wait” mode following a coldstart during the first Mast task. This is require by the M580 to diagnose the status of the Hotstandby system before to be operational.
In the configuration screen of the CPU, there is a menu in which, user can define the sections which are execute during the “Wait” status.
If only the first section is process following a hotstart and cold start, %S21 must be used only in the first section.
If you use the %S21 in an other section, this system bit will be never detected at 1.
Solution:
So the best way to fix this problem consists to manage the %S21 inside the first section.
When we push on the reset button of the CPU, we realize a cold start so M580 start in Wait mode during the first Mast task…
If the customer realize a Stop/Run on the CPU by using Unitypro, then all the sections are process because the M580 doesn't move in wait during the first Mast task (because the status of the second CPU is already known).
In standalone M580 CPU, the behavior is more classical, because the CPU don’t have to diagnose the Status of the Standby so the CPU don’t start in Wait…
In M580 Hotstandby system each CPU is starting all the time in “Wait” mode following a coldstart during the first Mast task. This is require by the M580 to diagnose the status of the Hotstandby system before to be operational.
In the configuration screen of the CPU, there is a menu in which, user can define the sections which are execute during the “Wait” status.
If only the first section is process following a hotstart and cold start, %S21 must be used only in the first section.
If you use the %S21 in an other section, this system bit will be never detected at 1.
Solution:
So the best way to fix this problem consists to manage the %S21 inside the first section.
When we push on the reset button of the CPU, we realize a cold start so M580 start in Wait mode during the first Mast task…
If the customer realize a Stop/Run on the CPU by using Unitypro, then all the sections are process because the M580 doesn't move in wait during the first Mast task (because the status of the second CPU is already known).
In standalone M580 CPU, the behavior is more classical, because the CPU don’t have to diagnose the Status of the Standby so the CPU don’t start in Wait…