PBP projects for R/C models

[mackrackit]

Mackrackit,
From what I understand your code will do a PWM every time TMR0 overflows.

The code in post #73 will toggle a LED when TMRO overflows. The LED on PORTD.7 will gradually become brighter then turn off and start over again.

This was just an example of an interrupt working with something else going on.

You do have to be careful with this as things will sometimes not work as expected. Like they say, the machine will do what it is told, not what you want

This is the same code as in post #73 with some modifications to demonstrate a "pitfall".
The START loop still has PORTD.7 PWMing the LED with PORTD.0 added to be toggled.
Inside of the interrupt loop the same PWM that is on PORTD.7 is now on PORTD.6.

What do you think will happen?
What does happen?

'16F887 INT RUPT
'44 PIN DEMO BOARD

 @ __config _CONFIG1, _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_OFF & _LVP_OFF & _CP_OFF

 INTCON.5 = 1    'ENABLE TMR0  DATA SHEET SECTION 14.3.2
 OSCCON = %01110000 '8 Mhz
 OPTION_REG = %10000111  ' 1:256 PRESCALE
 ON INTERRUPT GOTO TLOOP
 CNT  VAR BYTE
 D    VAR BYTE
 D = 0
 HIGH PORTD.0
 PAUSE 500

 START:
 FOR CNT = 0 TO 150
 PWM PORTD.7,D,100
 D = D + 2
 NEXT CNT
 TOGGLE PORTD.0
 PAUSE 100
 GOTO START

 DISABLE
 TLOOP:
 INTCON.2=0 ' DATA SHEET SECTION 14.3.2
 TOGGLE PORTD.4
 FOR CNT = 0 TO 150
 PWM PORTD.6,D,100
 D = D + 2
 NEXT CNT
 RESUME
 ENABLE

[Kenjones1935]

Just like you said it would.

Now on to your next one. It compiles and works also. I see what it does. I need to figure out how.

Thank you!!

[Kenjones1935]

Can anyone point me to a definition of "prescaler".
What I thought it meant does not seem to jive with what I am seeing.

Ken

[Kenjones1935]

"Running Small Motors with PIC Microcontrollers" says, on page108

"A pre-scaler is applied to the system clock and affects the timer by slowing down the system clock as it applies to the timer. Normally the timer is fed by a fourth of the basic clock frequency, which is called Fosc/4. In a system running a 4 MHz the timer sees a clock running at 1 MHz. If the pre-scaler is set for 1:8, the clock will be slowed down by another eight times, and the timer will see a clock at 125kHz."

"The post-scaler setting determines how may overflows will go by before an interrupt is triggered."

If I pre-scale TMRO 1:256 I will get overflows at about 4K per second. If I add a post-scaler of 1:64 I will end up with about 62 interrupts per second.

Close enough for government work?

Ken

[Kenjones1935]

I just found in DS33023 section 11.6.

"There is only one pre-scaler available which is mutually exclusively shared between Timer 0 and Watchdog Timer."

So I have to count the 4000 Interrupts per second using a

FOR CNT To 80
NEXT

loop. That will give me much closer to 50 pulses per second.

Correct?

[rmteo]

See my post #84 above. Which part is unclear to you?

[mackrackit]

Hi Ken,

I always get confused with this part of things too, so I will just point you to a couple of threads that I refer to when the need arises.

I think maybe the parts about
TMR1L
TMR1H
are the things you need to look at???

http://www.picbasic.co.uk/forum/showthread.php?t=961
http://list.picbasic.com/forum/messa...tml?1049090059