how to create a Digital Logic circuit for more than and less than in 8bit data?

ikelectro · Aug 31, 2012

Recently I'm working with a project. there I need tow logic that will determin whether the 8 bit data is 100 or more than 100 and 200 or more than 200. can you guys help me out?

Ian Rogers · Aug 31, 2012

Software or hardware logic?..... Software logic is easy...

ikelectro · Aug 31, 2012

Ian Rogers said:
Software or hardware logic?..... Software logic is easy...

obviously, iwant a hardwere logic using digital ICs.....

ericgibbs · Aug 31, 2012

ikelectro said:
obviously, iwant a hardwere logic using digital ICs.....

hi,
Look at the HEF4585 4bit magnitude comparator.

ikelectro · Aug 31, 2012

ericgibbs said:
hi,
Look at the HEF4585 4bit magnitude comparator.

yes. it'll works. if problem happen i'll known you.

ikelectro · Aug 31, 2012

View attachment 66819
in this ciruit, i'm able to one set of data is greater than or equal.
but i want two sets of data to compare in this automaticaly. it may be 100 and 200. plz frndz help with this.

ericgibbs · Aug 31, 2012

ikelectro said:
View attachment 66819
in this ciruit, i'm able to one set of data is greater than or equal.
but i want two sets of data to compare in this automaticaly. it may be 100 and 200. plz frndz help with this.

The easy way is to have two circuits , one for 100 and one for 200.
Connect the 'unknown 8 bits' to both circuit inputs and 100 to one circuit and 200 to the other circuit

Remember you have 4 states, so you need 4 LED's, so you will need some logic on the = > < outputs.

= 100
> 100
= 200
> 200

ikelectro · Aug 31, 2012

ericgibbs said:
The easy way is to have two circuits , one for 100 and one for 200.
Connect the 'unknown 8 bits' to both circuit inputs and 100 to one circuit and 200 to the other circuit

Remember you have 4 states, so you need 4 LED's, so you will need some logic on the = > < outputs.

= 100
> 100
= 200
> 200

but i want it in small circuit. not a big one. if i use 4 ICs, then the circuit'll be a big one.

crutschow · Aug 31, 2012

ikelectro said:
but i want it in small circuit. not a big one. if i use 4 ICs, then the circuit'll be a big one.

Then you need to do it with a microprocessor.

Hayato · Aug 31, 2012

Or you could draw a state-machine with 8-bit input.
If input = 100 it would output A.
For inputs [101 OR 102 OR...OR 199] it would output B
For inputs [200 OR....OR 255] it would output C
For inputs [0 OR....OR 99] it would output D

ikelectro · Aug 31, 2012

Hayato said:
Or you could draw a state-machine with 8-bit input.
If input = 100 it would output A.
For inputs [101 OR 102 OR...OR 199] it would output B
For inputs [200 OR....OR 255] it would output C
For inputs [0 OR....OR 99] it would output D

plz elaborate the technique of state-machine. bcz i dnt knw this.
and in that case it'll be and its circuit?

Ian Rogers · Sep 1, 2012

I have seen this done with an Eprom 27c64 before.... You can program the eprom so that every address above 100 = X then every location over 200 = Y.

This way you will be able to test ANY number.... Just connect your 8 bit data to the address bus... output on the databus..... or use a PLA..

ikelectro · Sep 1, 2012

Ian Rogers said:
I have seen this done with an Eprom 27c64 before.... You can program the eprom so that every address above 100 = X then every location over 200 = Y.

This way you will be able to test ANY number.... Just connect your 8 bit data to the address bus... output on the databus..... or use a PLA..

thats a great thinking..thanks a lot.

Hayato · Sep 1, 2012

ikelectro said:
plz elaborate the technique of state-machine. bcz i dnt knw this.
and in that case it'll be and its circuit?

As Ian said, you can use a ROM for that, to implement a truth table.

ikelectro · Sep 1, 2012

Hayato said:
As Ian said, you can use a ROM for that, to implement a truth table.

ok. i'll do.

ccurtis · Sep 1, 2012

You can do it with two ICs if you don't need the =100 or =200 outputs.

ikelectro · Sep 2, 2012

ccurtis said:
You can do it with two ICs if you don't need the =100 or =200 outputs.

ok. i'll look after it.. thanks...

WTP Pepper · Sep 3, 2012

I have no idea what your application is but if you could be a little more flexible with your values then it's very easy.
>127, >127 < 192, >192 is simple logic gates.
Digital hardware doesn't tend to be decimal friendly.

A PIC 16F5 series, ATMEL or other cheap CPUs will sort this out in a few lines of code as oppose to what could be a few large chips. It's also flexible in that you can change it at a later day without expensive hardware redesign. For simple logic of this kind, the only benefits are flexible power supplies and low current (4000 CMOS). Otherwise such logic is a waste of board space.
Time to move with the flow of engineering. PICs are readily available in India.

ikelectro · Sep 3, 2012

WTP Pepper said:
I have no idea what your application is but if you could be a little more flexible with your values then it's very easy.
>127, >127 < 192, >192 is simple logic gates.
Digital hardware doesn't tend to be decimal friendly.

A PIC 16F5 series, ATMEL or other cheap CPUs will sort this out in a few lines of code as oppose to what could be a few large chips. It's also flexible in that you can change it at a later day without expensive hardware redesign. For simple logic of this kind, the only benefits are flexible power supplies and low current (4000 CMOS). Otherwise such logic is a waste of board space.
Time to move with the flow of engineering. PICs are readily available in India.

yes i agree with your opinion. but im new in the fields of electronics, just cross 1 year with it. so its very hard to get touch with microcontroller at that time... but im preparing for that. so i also wrote a thread how to start learning micro....

WTP Pepper · Sep 4, 2012

Ian Rogers said:
I have seen this done with an Eprom 27c64 before.... You can program the eprom so that every address above 100 = X then every location over 200 = Y.

This way you will be able to test ANY number.... Just connect your 8 bit data to the address bus... output on the databus..... or use a PLA..

This is a good way but I dismissed on the grounds of size which the OP says is important. A 2764 is a huge IC, physically.

how to create a Digital Logic circuit for more than and less than in 8bit data?

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