Adder

brokenladder · Mar 15, 2007

How can I make an adder (adds two integer numbers) by only using contacts and coils?

It needs to add a number in N7:0 with N7:1 and place it in N7:2.
This is in RSLOGIX 500.

Thanks.

bernie_carlton · Mar 15, 2007

For inspiration, find the datasheet for a 'full adder' IC. Perhaps a 74LS83 would be a good start. Don't have a heart attack though when you see the equivalent logic.

Steve Bailey · Mar 15, 2007

Why you you want to limit yourself to contacts and coils when there are math instructions to do the job?

brokenladder · Mar 15, 2007

Steve Bailey said:
Why you you want to limit yourself to contacts and coils when there are math instructions to do the job?

its just required i do it that way

tvey · Mar 15, 2007

Here's a hint: think about your problem in binary...

For example, write out a simple test case like "3 + 2 = 5"

00000011
+ 00000010
----------
= 00000101

What is the result when BOTH your input bits are TRUE or when BOTH your input bits are FALSE?

What is the result when only one of your input bits are TRUE?

Don't forget the 16-bit overflow case..

I'm not sure you'd ever want to roll your own adder like this, but you can definitely apply the same principle for something like Gray Code to Binary conversion (for an encoder, for example).

-Trevor

bernie_carlton · Mar 15, 2007

I'm sure brokenladder is required to do the raw logic in pure contact and output format. No math blocks. I really meant it about being prepared when yoou see the equivalent logic from an 'adder' IC.

brokenladder · Mar 15, 2007

Ya thanks, but I cant use the adder function. I need to do it the hard way with only contacts and coils.

jvdcande · Mar 15, 2007

brokenladder said:
its just required i do it that way

I'm pretty sure this is a homework assignment.

Tip 1: it will require 16 equal networks to do the adding-up and an equal number of equal networks to carry the bits over.

Tip 2: analyse what you're doing when you add up two 16-bit binary numbers on paper.

Kind regards,

Ken Roach · Mar 15, 2007

Calling Don Lancaster

Any ordinary programmer would simply use the ADD instruction in the SLC-500. This is assuredly a class project to learn about binary arithmetic and how controller (and microprocessor) instruction sets encapsulate math functions.

What you're looking for, brokenladder, is called a "Binary Adder".

http://en.wikipedia.org/wiki/Adder_(electronics)

Start with a half-adder, then build a full-adder, then take a shot at a full fifteen-bit carrying adder.

brokenladder · Mar 15, 2007

ya it is a problem. i think i have a direction now. thanks.

brokenladder · Mar 15, 2007

I turned a full adder into ladder logic but do I need to apply the ladder logic for all 16 numbers(bits)?

OZEE · Mar 15, 2007

Only if you want a full 16-bit result. If you don't do all 16 bits, you won't get the right answer.

Don't forget to deal with the carry-bit.

Adder

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