Simple question - what does system bit SB90 do?
It does not have a description in VisiLogic but it is next to SB 91 which is "I/O Exp. Module--Command buffer is full" so based on this and on my tests I think it has something to do with I/O Module too.
Why am I interested in this?
Well - I have 2 sets as mentioned in Topic description:
- the first one is on site and is working hard
- the second one is on my desk and I make it suffer
As I tested with the one on the desk:
- SB90 is "0" when I have I/O module configured in HW configuration, everything is connected correctly and PLC is in run mode.
- SB90 is "1" when I have I/O module configured in HW configuration and disconnect I/O module during PLC running
or
when I have I/O module configured in HW configuration and PLC is starting (eg. after restart) with no I/O module connected
Of course when I disconnect I/O module from PLC, every DI and every AI is not read from I/O module by PLC.
My concern is that, at the moment, as I read the PLC running on site, SB90 is "1" but I get all the signals from I/O module.
I started this tests because I had problem with the PLC on the site - it had just stopped and, as guy working there told my on the phone, You could see Unitronics written on the HMI panel.
After restarting PLC (hard way - pluging the power off) everything was ok again.
So what does that SB90 really mean? If it is somehow connected with I/O module - it would really help me, if I would have known what way it is connected.
Any ideas?