SLC 5/03 S:24 indexed address fault

Hi everyone, I've got an SLC 5/03 that's suddenly started doing some funny things. I'm wondering if it might indicate the PLC is failing.

When S:24 has a value of -1, data table shows all bits high (1111111111111111). Does this mean it actually has a value of 65535?

Also, if we had an address #N97:0 when S:24 = -1, wouldn't this result in a major fault because it's out of N97 range?

It's worked for years until now and the value -1 is integral to the PLC logic working, I just don't understand how.

When S:24 has a value of -1, data table shows all bits high (1111111111111111). Does this mean it actually has a value of 65535?

Click to expand...

No, bit 15 is a sign bit.

http://www.binaryconvert.com/result_signed_short.html?decimal=045049

Also, if we had an address #N97:0 when S:24 = -1, wouldn't this result in a major fault because it's out of N97 range?

Click to expand...

No, a sign integer has a range of -32768 to +32767.

Can you tell the forum what the fault code is? (under processor status, error tab)

Ah that makes more sense.. thanks Mickey.