Reference time/clock help

[David Harper]

I'm trying to mesh two microcontrollers that need to sample separate
data at a relatively fast rate (one at 50 samples/sec, the other at
150 samples/sec). In order to determine what events logged by one
microcontroller corrospond to events logged by the second
microcontroller, I'm hoping to insert some sort of reference time (not
nessesarily in seconds, possibly in "counts") that they can both
access in order to timestamp the data before putting it on an eeprom.
I imagine this would require a parallel interface, but am not familiar
with alot of options out there.

What "viable" (aka relatively cheap and easy) options are there for a
fast reference clock for both chips? Can I just get a 555 hitting up
a counter? (Ideally, I'd like the "unit" of the timer to in the range
of 1/100th of a second or less, but 1/10th is doable).

Thanks in advance!
Dave

 

[Active8]

On 23 Nov 2004 12:34:39 -0800, David Harper wrote:

I'm trying to mesh two microcontrollers

?

that need to sample separate
data at a relatively fast rate (one at 50 samples/sec, the other at
150 samples/sec). In order to determine what events logged by one
microcontroller corrospond to events logged by the second
microcontroller, I'm hoping to insert some sort of reference time (not
nessesarily in seconds, possibly in "counts") that they can both
access in order to timestamp the data before putting it on an eeprom.
I imagine this would require a parallel interface,

?

but am not familiar
with alot of options out there.

Serial EEPROM might be what you want if you need external storage.

What "viable" (aka relatively cheap and easy) options are there for a
fast reference clock for both chips? Can I just get a 555 hitting up
a counter? (Ideally, I'd like the "unit" of the timer to in the range
of 1/100th of a second or less, but 1/10th is doable).

The uC should have timers/counters to use on-board. You can use an

external timer input. Drive it with anything, really. Two spare
inverters as an oscillator. CMOS 555. Full-wave rectified AC squared
up. Some PICs have an Fosc/4 output.
--
Best Regards,
Mike

 

[David Harper]

kensmith@green.rahul.net (Ken Smith) wrote in message news:<co0ul9$apr$1@blue.rahul.net>...

Many micros contain counters. If you arrange it so that one micro can
turn on the reference clock, at power up, both can clear the counters and
then after a short delay, one of the micros can start the reference clock.

Eh, ok, I didn't want to say it, but they're basic stamps, which do
not have timers/counters for accurate timekeeping (especially since
they can't multitask). Therefore I'm hoping to set up a peripheral
circuit that can be polled by both to get a timestamp (again, it
doesn't have to be in seconds, but can be in counts). Ideally, each
count would be down around the 1/100th second range, and it could
record atleast 10 seconds before reseting/rolling back to 0.

Thanks for the suggestions, and for any additional advice!
Dave

 

[David Harper]

Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote in message news:<d7g9q0he1b7r69urov1h9gdb1an6esn61g@4ax.com>...

Do they have I2C interface? You can get RT clocks with I2C..


Best regards,
Spehro Pefhany

Yeah, I'd seen some of those with 3-wire/SPI interfaces (I guess
that's I2C?), but they apparently only keep track down to the second
or quarter second. The more accurate ones are $$$. I may just use a
counter with a 555 hitting it every few seconds.

Thanks!
Dave