counters

[acy]

Hi there,

I am reviewing some digital stuffs done about 10 years ego in order to take a more advanced courses in mid-january. I need some help: how can I design a counter that counts the number of times the number 5 appears in an 4-bit input stream.

Note: NumberIn : 4-bits wide (input)
Start: Reset counter and overflow flag to zero while start is high (input)
Count: 8-bit unsigned count (of the number of “5”s that have occurred since start went
low (output)
Overflow: Goes high if count overflows (count is unsigned, so you only need to monitor
the adder carry out) and stays high until reset is asserted.

Thank you.

acy.

 

[4pyros]

OK thats an odd ball question. What would this be used for?

Decode the 4 bit stream with gates or a BCD to decimal counter and count the output with a counter chip.

Andy

 

[acy]

That was quick!
I jsut find the question in the book. And I noticed that by doing it I would learn a little bit more. Could you give me some more explaination or just scratch something out for me. I need to undersdand and work it out step by steps.

Thank you Andy.

 

[4pyros]

Start looking Here **broken link removed**

 

[4pyros]

Input 4 bits to a 4028 - BCD to decimal (1-of-10) decoder. Use the 5th output only and count it with a SN74HC590 8 bit counter. Andy

 

[acy]

Andy, sorry to ask you this but I was wondering if you could break it down to the gate level not the IC level because I really need to understand how to design it.

Thank you.

 

[ljcox]

You need to design a simple gating circuit using NAND or NOR gates to detect 0101.

Then use the output to clock a counter. But you will need to avoid counting the decoding spikes.

See my gating paper attached.