# Homework Help: Modulo 2 long division attempts

1. Mar 22, 2013

### fran1942

Hello, could someone please confirm if have done the modulo 2 division in order to find the CRC code word for these two correctly.

1) using the CRC polynominal 1011, for the information word 0101 1001
(attached image 1 is my attempt)

2) using the CRC polynominal 1101, for the information word 0100 1101
(attached image 2 is my attempt)

Thank you kindly for any confirmation.

#### Attached Files:

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• ###### problem2.jpg
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2. Mar 22, 2013

### Dick

You can check these by converting to decimal. For the first one, 1011001000 is 712, 1011 is 11. 712/11 is 64 remainder 8. You got 65 remainder 3. I'll give you a hint where you went wrong. 1000-1011 isn't 11. It's negative.

3. Mar 22, 2013

### fran1942

hello, thanks kindly for your help.
However, I just can't see what I have done wrong with that final operation on the first question.
I ended up with remainder 11 after I performed the XOR operation on 1000 and 1011.
How could I get another result. I thought the rule with modulo 2 division was to use XOR ?

Thanks for any clarification.

4. Mar 23, 2013

### rcgldr

It is, and CRC's use the same type of math. Your answers look OK to me.