RTC Chip

Started by p_dubinsky April 22, 2004
Does anyone know of a serial interface (SPI, i-Wire, etc), real time
clock chip that returns milliseconds? I don't need date but I do need
fractional seconds, ideally milliseconds.

TIA,
Paul



The spec on the DS2404 says it counts in 1/256 seconds. That's about
every 4 ms <g>

On Thu, 22 Apr 2004 22:15:46 -0000, p_dubinsky <>
wrote:

> Does anyone know of a serial interface (SPI, i-Wire, etc), real time
> clock chip that returns milliseconds? I don't need date but I do need
> fractional seconds, ideally milliseconds.
>
> TIA,
> Paul



Do you need a Real Time Clock or would a timer chip do?

On Thu, 22 Apr 2004 22:15:46 -0000, p_dubinsky <>
wrote:

> Does anyone know of a serial interface (SPI, i-Wire, etc), real time
> clock chip that returns milliseconds? I don't need date but I do need
> fractional seconds, ideally milliseconds.
>
> TIA,
> Paul




At 08:16 PM 4/22/2004, you wrote:

>Do you need a Real Time Clock or would a timer chip do?

Probably. I'm looking for elapsed time between events and I need about I
need resolution down to about 2 milliseconds. The max time between events
would be less than 10 minutes with no need for date or even hours for that
matter.

Paul >On Thu, 22 Apr 2004 22:15:46 -0000, p_dubinsky <>
>wrote:
>
> > Does anyone know of a serial interface (SPI, i-Wire, etc), real time
> > clock chip that returns milliseconds? I don't need date but I do need
> > fractional seconds, ideally milliseconds.
> >
> > TIA,
> > Paul >
>Yahoo! Groups Links >
>
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The resolution of the GetTime function on the BX-24 and BX-35 and BX-01(?)
is 1.95ms (1/512)

The only catch is that some system calls can stop the clock for short
times. But if you avoid them you should be good to go.

Bob Roos

On Thu, 22 Apr 2004 20:48:28 -0400, Paul Dubinsky <>
wrote:

> At 08:16 PM 4/22/2004, you wrote:
>
>> Do you need a Real Time Clock or would a timer chip do?
>
> Probably. I'm looking for elapsed time between events and I need about I
> need resolution down to about 2 milliseconds. The max time between events
> would be less than 10 minutes with no need for date or even hours for
> that
> matter.
>
> Paul >> On Thu, 22 Apr 2004 22:15:46 -0000, p_dubinsky <>
>> wrote:
>>
>> > Does anyone know of a serial interface (SPI, i-Wire, etc), real time
>> > clock chip that returns milliseconds? I don't need date but I do need
>> > fractional seconds, ideally milliseconds.
>> >
>> > TIA,




At 10:46 PM 4/22/2004, you wrote:

>The resolution of the GetTime function on the BX-24 and BX-35 and BX-01(?)
>is 1.95ms (1/512)
>
>The only catch is that some system calls can stop the clock for short
>times. But if you avoid them you should be good to go.

Actually, that's exactly my problem: I'm using the pulsein command to
measure the timing of two different events and I can lose up to 71 ms for
each pulsein command if the event doesn't take place (a possibility). That
blows all of the built in time functions (GetTime, Timer) out of the water.
Right now I keep a running total of the losses from the pulsein command in
a variable, TimerOffset, and when I need to get the time of day (actually
the time since startup), I use the Timer function, add the TimerOffset
value and then calculate the hours minutes and seconds. It's not very
elegant and pretty slow, too.

What I'm looking for is a timer that's not affected by the Pulsein command
and has a resolution as good as the native 1.96ms resolution.

Thanks,
Paul >Bob Roos
>
>On Thu, 22 Apr 2004 20:48:28 -0400, Paul Dubinsky <>
>wrote:
>
> > At 08:16 PM 4/22/2004, you wrote:
> >
> >> Do you need a Real Time Clock or would a timer chip do?
> >
> > Probably. I'm looking for elapsed time between events and I need about I
> > need resolution down to about 2 milliseconds. The max time between events
> > would be less than 10 minutes with no need for date or even hours for
> > that
> > matter.
> >
> > Paul
> >
> >
> >> On Thu, 22 Apr 2004 22:15:46 -0000, p_dubinsky <>
> >> wrote:
> >>
> >> > Does anyone know of a serial interface (SPI, i-Wire, etc), real time
> >> > clock chip that returns milliseconds? I don't need date but I do need
> >> > fractional seconds, ideally milliseconds.
> >> >
> >> > TIA, >
>
>Yahoo! Groups Links >
>
>---
>Incoming mail is certified Virus Free.
>Checked by AVG anti-virus system (http://www.grisoft.com).
>Version: 6.0.665 / Virus Database: 428 - Release Date: 4/21/2004

===========================================================
"We have the power to do any damn fool thing we want to do,
and we seem to do it about every ten minutes."
J. William Fulbright , quoted in Time (New York, Feb. 4, 1952).
===========================================================

---------- ---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.665 / Virus Database: 428 - Release Date: 4/21/2004



> ... What I'm looking for is a timer that[] has a resolution as good as
the native 1.96ms resolution.

And a range of (10 minutes) 600000mS or a 20-bit millisecond counter.
I'm not aware of a drop-in part, but that would be a trivial PIC
application with the right crystal or an external oscillator/divider.

You can do the same in discrete logic and either latch and shift the
count in or perhaps count 8 bits externally and count overflows from it
in BX-24 code (you'd also need to get the LSB 8 bits at T1, either
shifted or via eight or five [4 + a 1 bit selector output] pins). If
the processor is doing little else you can also count a 1KHz external
signal in BX-24 code, of course. Tom
Tom Becker
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