slc 500 questions

[michael childers]

If I add the memory module for slc 5/04 and go into memory
under processor and set to a 1 to load at boot.
question is that all I have to do as I have one location in
the program that has a rung in the program that latches the
bit.
and also there is a rung to unlatch errors on overflow trap.

never saw in logic where it latched and unlatched stuff with
status bits.
Is this common and I need to do it to use the memory module or
if I install one and it boots does it automatic use it?
Thanks ahead of time for any and all responses.

 

[JesperMP]

It is not normal to use the "load always" bit. That will mean that the current values in all files will be lost on every powerup.
It is more common to use the "load on memory error" bit. In that case the program will load only if the battery backed program has been lost or is corrupted.

The bits to load from the memory module should be set in the CPU status file. Do not set or reset the bits in code (!). If one of the bits gets set and the memory module is not installed, then the CPU will fault and you can then not clear the bits by code (because the CPU is faulted) = catch-22.

To unlatch the overflow trap bit is very common, and IMHO better than to let the CPU fault because of a trivial counter overrun or similar. But as a minimum the overflow bit should trigger an HMI alarm "math overflow detected in program" or something like that.

 

[michael childers]

so there should not ever be anything written in code and just set bits in status file.
thanks

 

[JesperMP]

exactly.