DirectSoft 6 Math and negative results with BCD

Hi all,

I got thrown into a project using a D2-240 CPU, never used Directlogic or AD before this morning and am fumbling through it but have a few questions regarding AD's handling of negative math results using BCD format.

This is an upgrade/Modification to an existing project and I don't have access to the hardware to just test this out.

I don't need negative results but just wondering what happens if the calculation results in a negative number.

For example:
LD V2001
SUB V2022
OUT V2002

IF V2001 = 10
V2022 = 5

V2002 will equal 5

What happens when
V2001 = 5
V2022 = 10

am i right to assume from my readings that
V2002 will = 5
With SP70 being set to 1
or will it cause a fault


again I am not familiar with this brand, I usually only with with the Logix 5000 platform, and am under the gun to get this done as I am the 'PLC Guy' and am supposed to show up to site with the program working and this is the only thing really holding me up at this point

Thanks in Advance

I occasionally have to deal with the possibility of negative results. If it looks likely I do an inline comparison of the two operands to affect a bit. Then I use the bit to determine the later actions. I'm not sure about the resultant flags. The result would be interpreted as a very large number.

Thanks Bernie

I kind figured I would have to go that route

If you think the number might go negative, you really should convert to Binary or Real data types before doing any math. Then you can check the upper bit to see if it is on (negative) before reconverting back to BCD.

Correct me if I am wrong but I don't think I can do anything but BCD math on the 240 processor

You are correct. You can convert to Binary, but you cannot do the binary math...
Just put your SP70 immediately below your SUB instruction, so that you can respond accordingly.

You are correct. Just shows how long it's been since I have actually programmed a D2-240.