James,
     That depends on how much money that I want to spend. The crystals=20
that you supply your own caps for and the 4 pin canned crystals look=20
like they have a stability of +- 10 to +-100 ppm. You can get temp=20
controlled crystals that have a stability of +-10 ppb but these are a=20
lot more expensive. Maxim makes a great little 32KHz osc module that is=20
+-2ppm. So without buying a temp controlled osc I would be looking at=20
best about +- 5 to 10 ppm. So that puts me in the range of less than 1=20
percent but not as good as 1ppm. That would be ok. It would make a nice=20
little hobby and experimenter counter.
     Yes, but that is the part that I don't know how to do. How do I=20
setup the timer or timers so that when I want it to it will output a 1=20
second pulse to open the counter control gate?
     The ADC would read the pot to tell how long the operator wants to=20
display the reading before the next update takes place.
Thanks,
rich!

On 7/18/2014 4:41 AM, James Cameron wrote:
> On Fri, Jul 18, 2014 at 03:47:44AM -0500, Richard R. Pope wrote:
>>       Less than 1 percent would be worst case. If 1ppm could be achieved
>> that would be great but I don't know if that is possible. I'm not going
>> to use it for calibration work.
> But what is your crystal accuracy?
>
> On Fri, Jul 18, 2014 at 04:12:37AM -0500, Richard R. Pope wrote:
>> James,
>>       My HP gets 1ppb of course I don't expect any thing close to that.
>> Like I said 1ppm would be great. OK, no resonator. A crystal is no
>> problem. Timers sound better but more difficult. And it is the timer
>> that I don't how to setup to get my one second pulse on demand.
> A timer is a counter.  Unlike a software counter, it counts by itself.
>
> So your software would load a reset value into the counter, reset the
> counter, enable the interrupt, wait for the interrupt, and when the
> interrupt occurs generate the pulse.
>
> Some timers have to be reset, some timers have an autoloading reset
> value.  The datasheet for the part will tell you.
>
>>       The reset pulse is easy. Just output the high for one or two
>> instruction cycles. The part that I'm not getting is how to wait for
>> whatever amount of time that corresponds to the wishes of the user for
>> the length of time to display the reading. Sometimes when I am using my
>> HP freq counter I like to have a very fast display refresh. At other
>> times I want the count to stay up for a much longer time period before
>> it is refreshed.
>>       The reset pulse of 20ns or longer occurs when the display should b=
e
>> refreshed. Then the one second pulse is output to open the count gate.
>> Now we wait for a certain length of time so that the user can read the
>> display and then we output the reset pulse and open the counting gating
>> and do this over and over. But how? I know what I want to do and the
>> order to do them in but I don't know how. I know that the configuration
>> fuses have to be set, then setup the ADC, setup the timer or timers, and
>> finally enter the loop. Is that it?
> Not sure what you want an ADC for, sorry.  Maybe I missed something.
>

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