DirectSoft 5 assistance

subjwd · Oct 23, 2009

Please see the attached picture. I'm new to AD, but not PLC's.

I'm trying to subtract V20000 from V20002 and put it in V22000.

From the data table, I expect a value of 10550, but I get 54847, the same value as V20002.

Can anyone tell me what I'm doing wrong? Thanks!

jstolaruk · Oct 23, 2009

Don't know AD stuff but those values are not within the range of a signed 16bit Word and may cause a overflow, underflow minor fault killing the instruction. Can you move up to double-word variables?

Brian123 · Oct 23, 2009

You are working with hex (aka binary) formatted numbers, not BCD numbers. To perform math on hex numbers, you need to use use the binary math commands. In this case, replace the SUB with SUBB.

The original SUB instruction was expecting a BCD number. When it saw a hex number it freaked out and froze like a deer in the headlights and did nothing.

Brian

subjwd · Oct 23, 2009

Just to test that out, I tried values of 50 and 30, expecting difference of 20. Result was still 30.

subjwd · Oct 23, 2009

That's it Brian. Knew it had to be something simple.

Thanks everyone!

Brian123 · Oct 23, 2009

jstolaruk said:
Don't know AD stuff but those values are not within the range of a signed 16bit Word and may cause a overflow, underflow minor fault killing the instruction. Can you move up to double-word variables?

AD really doesn't have a signed 16bit data type, at least not a native one. You can always write the program to interpret the register as a signed word, but the instructions don't handle it for you. If you want native signed numbers, you need to jump to reals.

Brian

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