Confusion about RTCC timing in the manual

[hillcraft]

<font face="Courier New" size=-1>On page 188 of the CCS manual in demo EX_STWT.C the following appears.

#use delay (clock=20000000)
#define INTS_PER_SECOND 76 // (20000000/(4*256*256))

===in code
setup_counters (RTCC_INTERNAL,RTCC_DIV_256);

Is this correct:
20000000/4 = 5000000 -> internal clock
5000000/256 = 19531.25 -> RTCC roll over
19531.25/256 = 76.294 -> RTCC_DIV_256
===========================================
This is wher I get confused
On page 136 of PICmicro MCU C by Nigel Gardner the following appears;

#use delay(clock=1024000)

===in code
setup_counters(rtcc_internal,rtcc_div_256);
// increments 1024000/4*256 times per second
//or every millisecond

Is this correct:
1024000/4 = 256000 -> internal clock
256000/256 = 1000 -> RTCC roll over

-- this part of the calculation is not performed
1000/256 = 3.9 -> RTCC_DIV_256
===========================================

My question is: is the example in Nigel Gardner's book incorrect because the RTCC_DIV_256 is never taken in to account?</font>
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516638

[Felix Althaus]

Hello

:=#use delay (clock=20000000)
:=#define INTS_PER_SECOND 76 // (20000000/(4*256*256))
:=
:====in code
:=setup_counters (RTCC_INTERNAL,RTCC_DIV_256);
:=
:=Is this correct:
:=20000000/4 = 5000000 -> internal clock
:=5000000/256 = 19531.25 -> RTCC roll over
:=19531.25/256 = 76.294 -> RTCC_DIV_256
:============================================

Yes, I think your calculation is correct

:=This is wher I get confused
:=On page 136 of PICmicro MCU C by Nigel Gardner the following appears;
:=
:=#use delay(clock=1024000)
:=
:====in code
:=setup_counters(rtcc_internal,rtcc_div_256);
:=// increments 1024000/4*256 times per second
:=//or every millisecond
:=
:=Is this correct:
:=1024000/4 = 256000 -> internal clock
:=256000/256 = 1000 -> RTCC roll over

The comment of the code sais something about incrementing every 1ms, so I think this 1000 is the incrementing frequency of tmr0 and not the roll over frequ.


:=-- this part of the calculation is not performed
:=1000/256 = 3.9 -> RTCC_DIV_256
:============================================
:=
:=My question is: is the example in Nigel Gardner's book incorrect because the RTCC_DIV_256 is never taken in to account?

I don't know this appliaction of M. Gardner but perhaps there is no tmr0-isr? And so he don't use the roll-over.

may this helps

mfg
Felix
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516641