How to design a system that includes two PLCs, one is master, and the other is its backup. While the master is terminated due to some problems, then the backup would start immediately?Basically the master can always send signal to backup as running and as long as the backup cannot receive the signal, that means something wrong with the master, then backup start to run. When the signal is back again, the backup goes to stop. Using MODRD/MODWR or RS instructions.
