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russk2txb
Joined: 30 Mar 2008
Posts: 109
Location: New Jersey
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| Timer clock |
 Posted: Thu Jan 13, 2011 2:15 pm |
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Maybe a dumb question, but I cannot find a clear answer. When using timer0 on RTCC, with #use delay(clock=40M, oscillator=10M), is the clock cycle 40M/4 or is it 10M/4 ?
Thanks, Russ |
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wind88
Joined: 29 Dec 2010
Posts: 37
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| Posted: Thu Jan 13, 2011 2:24 pm |
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| Code: | | Period = (256 - TMR0)*(4/fosc)*(Prescaler) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Jan 13, 2011 2:37 pm |
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The Timer0 is clocked at 1/4 of the PIC's oscillator speed. The oscillator
is running at 40 MHz, so the Timer is clocked at 10 MHz.
The fact that the oscillator speed is specified by the "clock=" statement
is given in the CCS manual:
| Quote: | #USE DELAY
Syntax: #USE DELAY (options))
Elements: Options may be any of the following separated by commas:
clock=speed speed is a constant 1-100000000 (1 hz to 100 mhz).
This number can contains commas. This number also supports the
following denominations: M, MHZ, K, KHZ. This specified the clock the
CPU runs at. |
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russk2txb
Joined: 30 Mar 2008
Posts: 109
Location: New Jersey
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| Posted: Thu Jan 13, 2011 3:16 pm |
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Thanks PCM. Maybe you can see why it is confusing. The equation says use 4/fosc, but it is really 4/clock (as used in the #use delay function).
Regards, Russ |
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gpsmikey
Joined: 16 Nov 2010
Posts: 588
Location: Kirkland, WA
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| Posted: Thu Jan 13, 2011 4:38 pm |
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Hey Russ don't feel bad - I've been bitten with that one before too. Somehow I either end up with too many or too few "/4"parts of my equation when figuring things out. 
mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3 |
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