double word help

[blglaw]

I am trying to use BCD_INT32 with my C-more micro graphic display to enter in a value for inches for a length measuring system.  I can enter the value into the display, 1234.56" but when the PLC looks at the same location, it sees 34.56".  I believe it needs to look at 2 Vmem locations.  How do i set the PLC to look at double word location?  I am using greater than/less than functions to compare  my lengths and slow down my motor and then stop.  Is this done in the Memory editor and with it then  look at both words?

[franji1]

Relationals only work with single word values.  There is a CMPD (Compare Double) box that will perform the operation, but as a function, not as inline contacts.  You will need to look at the SP60/61/62 to see the result of the comparison.  I recommend looking at Chapter 5 in the User Manual at the CMPD instruction description.

[MikeS]

you can use a pair of relational contacts - one comparing the upper v-memory location with the upper word of your value, the other comparing the lower v-mem with the low half of the value -  but that's very ugly and hard to maintain.

the best answer is to use the cmpd instruction with it's sp60, 61 & 62 bits to do the comparison. using math functions with sp bits isn't much better, but it's much more maintainable over the long haul.

[blglaw]

OK....thanks.  That is what i figured out.  I just have to get it to work now. 
Thanks again,
Bill