# Digital logic design

#### yagmai

Joined May 19, 2005
3
hi guys,

how to approach a logic design problem??

suppose I haf a IC which takes in 2 3-bit binary numbers, x2,x1,x0 and y2,y1,y0..
determines whether they are equal and which 1 is larger

there are 3 outputs defined as follows
1. M=1 only if 2 input numbers are equal
2. N =1 only if x2x1x0 is greater than y2y1y0
3 P = 1 only if y2y1y0 is greater than x2x1x0

how do u start doing this problem??

I gd at doing computer programming eg Java, C++..however logic design realli gif me headache

#### hgmjr

Joined Jan 28, 2005
9,029
You're in luck. The 74HC85 is a 4-bit magnitude comparator with the three output conditions you require.

All you need to do is tie the unused 4th bit on both of the 4-bit input ports together and then tie them high or low and you got it made.

Of course, if your object is to do the logic design yourself using common logic gates then you are also in luck since the schematic of the device included in the datasheet contains enough detail to get you off to a good start with your design.

Datasheet website

Just search on the generic part number 74HC85.

hgmjr