1 Counter/Multiple Clocks -or- Mixing 4 Clocks To 1 Clock

[Curtis]

Hi,

I've been trying to come up with a simple circuit to do the following:
Accept 4 clock
inputs and count the total number of pulses from each of the 4 clocks OR
take the
4 clock inputs and output a single clock I can use with a regular counter.

I have 4 square wave clocks that I want to count. They vary from about 3 KHz
to 40 KHz.
This is what they look like (excuse my drawing skills).

Clock 1: ____----____----____
Clock 2: -____----____----____
Clock 3: --____----____----____
Clock 4: ---____----____----____

You get the idea. None of the rising or falling edges will ever interfere
with each other.
However, there are times when one or more clocks may be off (held low) like
this:

Clock 1: ____----____----____
Clock 2: ___________________
Clock 3: --____----____----____
Clock 4: ---____----____----____

I want to end up with an accurate count of all the pulses from the 4 clocks.
Does anyone have a
simple solution to this? It's been driving me crazy but maybe I'm missing
the obvious.

Thanks in advance.

 

[Bob Monsen]

Curtis wrote:

Hi,

I've been trying to come up with a simple circuit to do the following:
Accept 4 clock
inputs and count the total number of pulses from each of the 4 clocks OR
take the
4 clock inputs and output a single clock I can use with a regular counter.

I have 4 square wave clocks that I want to count. They vary from about 3 KHz
to 40 KHz.
This is what they look like (excuse my drawing skills).

Clock 1: ____----____----____
Clock 2: -____----____----____
Clock 3: --____----____----____
Clock 4: ---____----____----____

You get the idea. None of the rising or falling edges will ever interfere
with each other.
However, there are times when one or more clocks may be off (held low) like
this:

Clock 1: ____----____----____
Clock 2: ___________________
Clock 3: --____----____----____
Clock 4: ---____----____----____

I want to end up with an accurate count of all the pulses from the 4 clocks.
Does anyone have a
simple solution to this? It's been driving me crazy but maybe I'm missing
the obvious.

Thanks in advance.

An XOR gate will change it's output whenever an input changes. If you
use an XOR gate for each pair of clocks, and feed the outputs into
another XOR gate, then if any time any of the clocks change, the output
will change. Thus, a counter which uses that as a clock will count the
pulses.

The problem with this is that if the clock input transistions occur too
close together, the input to the counter can change too quickly, and
violate the setup or hold times. Also, if clocks change together, you'll
miss a pulse.

I think this works. You may wish to take a few moments to verify it.

Regards,
Bob Monsen

 

[John Fields]

On Tue, 19 Apr 2005 01:11:06 GMT, "Curtis" <curtis@dangonay.com>
wrote:

Hi,

I've been trying to come up with a simple circuit to do the following:
Accept 4 clock
inputs and count the total number of pulses from each of the 4 clocks OR
take the
4 clock inputs and output a single clock I can use with a regular counter.

I have 4 square wave clocks that I want to count. They vary from about 3 KHz
to 40 KHz.
This is what they look like (excuse my drawing skills).

Clock 1: ____----____----____
Clock 2: -____----____----____
Clock 3: --____----____----____
Clock 4: ---____----____----____

You get the idea. None of the rising or falling edges will ever interfere
with each other.
However, there are times when one or more clocks may be off (held low) like
this:

Clock 1: ____----____----____
Clock 2: ___________________
Clock 3: --____----____----____
Clock 4: ---____----____----____

I want to end up with an accurate count of all the pulses from the 4 clocks.
Does anyone have a
simple solution to this? It's been driving me crazy but maybe I'm missing
the obvious.

Thanks in advance.

---


CLOCK1>---+-------------A
| AND Y-----A
+--[INVERT]---B OR Y------A
+--B OR Y---> Output to counter
CLOCK2>---+-------------A | +---B
| AND Y--+ |
+--[INVERT]---B |
|
CLOCK3>---+-------------A |
| AND Y-----A |
+--[INVERT]---B OR Y--+
+--B
CLOCK4>---+-------------A |
| AND Y--+
+--[INVERT]---B



This circuit generates slivers equal to the propagation delays of the
inverters at the outputs of the ANDs, so you may need to add a little
delay to the inverters to make sure the slivers last long enough to
make it through the ORs. Like this:



CLOCKn>---+--------------------A
| AND Y---
+--[INVERT]--[R]--+--B
|
[C]
|
GND

A few microseconds should be plenty.
--
John Fields
Professional Circuit Designer

 

[John Fields]

On Tue, 19 Apr 2005 08:15:20 -0500, John Fields
<jfields@austininstruments.com> wrote:

CLOCK1>---+-------------A
| AND Y-----A
+--[INVERT]---B OR Y------A
+--B OR Y---> Output to counter
CLOCK2>---+-------------A | +---B
| AND Y--+ |
+--[INVERT]---B |
|
CLOCK3>---+-------------A |
| AND Y-----A |
+--[INVERT]---B OR Y--+
+--B
CLOCK4>---+-------------A |
| AND Y--+
+--[INVERT]---B


---

Or, more simply:


CLOCK1>----[C]--+--[1N4148>]---+--->OUTPUT TO COUNTER
|K |
[1N4148] |
| |
GND |
|
CLOCK1>----[C]--+--[1N4148>]---+
|K |
[1N4148] |
| |
GND |
|
CLOCK1>----[C]--+--[1N4148>]---+
|K |
[1N4148] |
| |
GND |
|
CLOCK1>----[C]--+--[1N4148>]---+
|K |
[1N4148] [R]
| |
GND GND





--
John Fields
Professional Circuit Designer

 

[Tom Del Rosso]

"John Fields" <jfields@austininstruments.com> wrote in message
news:qkt9619d1o9q05he1esfgpf7a01t95v2sh@4ax.com...

CLOCK1>---+-------------A
| AND Y-----A
+--[INVERT]---B OR Y------A
+--B OR Y---> Output to counter
CLOCK2>---+-------------A | +---B
| AND Y--+ |
+--[INVERT]---B |
|
CLOCK3>---+-------------A |
| AND Y-----A |
+--[INVERT]---B OR Y--+
+--B
CLOCK4>---+-------------A |
| AND Y--+
+--[INVERT]---B

If you change those ORs to XORs it would at least reduce the chance of
missing a pulse because it overlaps with the pulse from another AND.

I think the only way to do it seriously is to have 4 counters and add them.
The Laws of Form could make a minimal solution with the same performance as
4 counters and adders, but it seems nobody ever figured out the Laws of
Form. I will re-read the book some day. Maybe a light bulb will go on.


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