PLCDirect Newbie

zmanvortex

Member
Join Date
Apr 2002
Location
Nebraska
Posts
216
I learned how to program plc's strictly on Allen Bradley equiptment at my local college. I learned how to use every single instruction and have done quite a few projects including a couple of motion control projects using the SLC platform. I now find myself at a place of employment which does not use A-B equiptment but rather PLCDirect equiptment. I have read all of the instruction manuals and can pretty much write a program without too much trouble.
The thing I am wondering about is the value that is stored in a memory address and manipulating this value. I know that in an A-B programming environment I can see the value in a number of different formats, including decimal, and the math instructions use the decimal format (including constants) which most humans are familiar with. In the PLCDirect environment the closest I can get to seeing a value in decimal format is BCD. I know that over time I will get used to using BCD but why not make it easier on the programmer and include decimal format. The other complaint I have is that I have to constantly load a value I want to manipulate or use into a thing called the accumulator. It just seemed like a lot less instructions to program an Allen Bradley unit compared to the PLCDirect unit.
One of the things I did like about the PLCDirect is the use of states. Even when I wrote programs for A-B platforms I used a state transition approach by latching and unlatching subroutines. PLCDirect makes this task easier by using states.
Will PLCDirect continue to use strictly BCD and continue to make you use an accumulator or do they have plans to change.
 
I very much doubt that PLC Direct (Now caled AutomationDirect.com) will change their format. The good news is, it isn't really a problem, and you can treat it like "decimal" most of the time.

If you want to see the number in different formats, open a Data View window. Enter the register(s) you want to monitor. Click on the field for the value, and at the top menu bar you can tell it to display as BCD/Hex, binary, etc. If you want to see the same number in different formats enter it twice and change the formats as desired.

The good news is you can treat the number as a decimal. In other words, if you take 2 x 6 and stick it in a register, the result will display as "12" and not as "C". If you then add 2, the result will display as 14, not as "E". The BCD is Binary Coded DECIMAL format, and if you start seeing "A" through "F" in the number it generally indicates and overflow or some spurious value is being written to it.

I do like the ability in the SLC to enter formulas and so forth, and the SCP instructions are convenient. However, we do a lot of math in the ADC platform, and once you get used to it it isn't really much trouble. You can always cut and paste a similar math block and just change the V-Memory registers. The only caution is if you do subtraction and get a negative number the result is two's complement and some "interesting" values get displayed and used. This is the biggest problem with the ADC math, and you occasionally end up with two diffent sets of math depending on which number is larger. We just do a compare, set a bit, and use it to dictate which rungs will execute.

(OOPS - Double post - sorry)
 
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