Skipping "zero" with a counter?

[eromlignod]

Hi guys:

I'm working on an application where I'd like to have a two-bit counter
that needs to continuously count 1, 2, 3, 1, 2, 3, 1, 2, 3... in a
loop. I don't want zero. It is controlling three of the four
channels of a mux and the zero channel is "off" (no signal), so I want
to skip it.

Is there an easy way to do this, or do I need to build my own counter
with logic?

Don

 

[John Popelish]

eromlignod wrote:

Hi guys:

I'm working on an application where I'd like to have a two-bit counter
that needs to continuously count 1, 2, 3, 1, 2, 3, 1, 2, 3... in a
loop. I don't want zero. It is controlling three of the four
channels of a mux and the zero channel is "off" (no signal), so I want
to skip it.

Is there an easy way to do this, or do I need to build my own counter
with logic?

Yes, and probably. Do you want a two bit binary
representation of the count sequence (01, 10, 11, 01 etc.)
or three individual bits that take turns turning on in
sequence (001, 010, 100, 001, etc.)? Do you need a reset
function to an initial count, or can the count start at any
point in the sequence? It is the details that determine the
simplest way to accomplish the counter.

--
Regards,

John Popelish

 

[John Fields]

On Wed, 26 Mar 2008 07:03:41 -0700 (PDT), eromlignod
<eromlignod@aol.com> wrote:

Hi guys:

I'm working on an application where I'd like to have a two-bit counter
that needs to continuously count 1, 2, 3, 1, 2, 3, 1, 2, 3... in a
loop. I don't want zero. It is controlling three of the four
channels of a mux and the zero channel is "off" (no signal), so I want
to skip it.

Is there an easy way to do this, or do I need to build my own counter
with logic?

---
You could use an 8 bit asynchronously presettable counter, like a 4510
or a 4516, and have it load 0001 when it counts to 0100: (view in
Courier)

+-------------+
| +---------+ |
+-|LOAD | |
|__ | |
GND>-+-O|CE | |
| | | |
+--|MR | |
| | | |
+--|D4 Q4| |
| | | |
+--|D3 Q3|-+
| | |
+--|D2 Q2|----->MSB OUT
| |
Vcc>-+--|D1 Q1|----->LSB OUT
| | _ |
+--|U/D |
| |
CLK>----|>CP |
+---------+

 

[Tim Wescott]

On Wed, 26 Mar 2008 07:03:41 -0700, eromlignod wrote:

Hi guys:

I'm working on an application where I'd like to have a two-bit counter
that needs to continuously count 1, 2, 3, 1, 2, 3, 1, 2, 3... in a loop.
I don't want zero. It is controlling three of the four channels of a
mux and the zero channel is "off" (no signal), so I want to skip it.

Is there an easy way to do this, or do I need to build my own counter
with logic?

Don

If you need a 2-bit binary counter, you can do this with a pair of J-K
flip flops and some wires. I don't know for sure, but I think you can
get just about _any_ 2-bit sequence you want from a J-K flip-flop pair
without additional logic.

(It would be interesting to know just how far this extends -- can you do
this with any three-bit sequence and three J-Ks? Four? Five?)

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

 

[John Fields]

On Wed, 26 Mar 2008 09:53:52 -0500, John Fields
<jfields@austininstruments.com> wrote:

You could use an 8 bit
/

/
Oops, 4 bit-----


JF

 

On 3ÔÂ26ČŐ, ĎÂÎç10Ęą03ˇÖ, eromlignod <eromlig...@aol..com> wrote:

Hi guys:

I'm working on an application where I'd like to have a two-bit counter
that needs to continuously count 1, 2, 3, 1, 2, 3, 1, 2, 3... in a
loop. I don't want zero. It is controlling three of the four
channels of a mux and the zero channel is "off" (no signal), so I want
to skip it.

Is there an easy way to do this, or do I need to build my own counter
with logic?

Don

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[Mike Silva]

On Mar 26, 11:26 am, Tim Wescott <t...@seemywebsite.com> wrote:

If you need a 2-bit binary counter, you can do this with a pair of J-K
flip flops and some wires.  I don't know for sure, but I think you can
get just about _any_ 2-bit sequence you want from a J-K flip-flop pair
without additional logic.

(It would be interesting to know just how far this extends -- can you do
this with any three-bit sequence and three J-Ks?  Four? Five?)

J-K flip-flops, what a blast from the past. Can't remember the last
time I needed them. But you're right, that's a very clean solution, a
single dual-FF package. I warmed up the long-forgotten neurons and
came up with this solution

Ja = B, Ka = B
Jb = 1, Kb = !A

I used to love solving those problems.