Darrel Taylor Interrupts and MultiCalc

[Demon]

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Click the leftmost icon above your post window; SWITCH EDITOR TO SOURCE MODE. Then go to advanced mode (below post window at right) to get the CODE icon.

Robert

[AvionicsMaster1]

Well, it's refreshing to learn something new. Anyway, here's the code that didn't come through earlier.

;This program will blink a light on portb.1 at a 1 hz rate   --
'with another LED on portd.1 blinking at a different rate
'different TMR1 preloads to get desired frequencies

wsave   VAR BYTE    $70     SYSTEM    ' alternate save location for W 
                                      ' if using $70, comment wsave1-3

wsave1  VAR BYTE    $A0     SYSTEM    ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM    ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM    ' location for W if in bank3

LED1   VAR  PORTB.1
led2   VAR portd.0

INCLUDE "DT_INTS-14.bas"    ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"    ' Include if using PBP interrupts
DEFINE osc20
ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  _ToggleLED1,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON = %00000001                ; Prescaler = 1:1, TMR1ON
@ INT_ENABLE  TMR1_INT     ; enable Timer 1 interrupts

preload VAR WORD

preload = 61476 '60543 by MultiCalc should yields about 200Hz but 
                '60643 yeilds exactly 100 Hz
                ' 48876 29.8cps
                ' 57209 yields 59.5cps
                ' 61376 yields 
                
tmr1l = preload.LowByte
tmr1h = preload.HighByte

Main:
  PAUSE 500
  TOGGLE led2
  PAUSE 500
  TOGGLE led2
  
GOTO Main

'---[TMR1 - interrupt handler]------------------------------------
ToggleLED1:
           t1con.0 = 0
           tmr1l = preload.LowByte
           tmr1h = preload.HighByte
           t1con.0 = 1
     TOGGLE LED1
@ INT_RETURN

[Demon]

I'm pretty sure PAUSE messes up the timer routines.

I think you're supposed to use FOR loops instead.

Robert


EDIT: Something like:

for loop = 1 to 500
    pause 1
next loop

[Darrel Taylor]

He's not using ON INTERRUPT Robert.

Greg,

It takes 2 interrupts to turn an LED On and Off. So 200hz interrupts produces a 100 hz flashing led.
If you want to keep time from 100hz interrupts, that would be too fast.

Since you want accuracy, you shouldn't just load the timer with a value.
It takes time to get to the interrupt handler, and the timer has been counting during that time.
If you just load a value into the timer, that amount of time is lost.

If you ADD the reload value to the current timer value, it no longer matters how long it took to get to the handler.
It also takes a certain amount of time to ADD the value to the time, and that time must be accounted for as well.

Take a stab at the "Timer Template" http://www.darreltaylor.com/DT_INTS-...rTemplate.html
It does all that stuff for you.

Use a prescaler of 1.

It should give exactly 100hz interrupts, down to the exact cpu cycle.
Close enough to be only a few seconds off after a month or two. Depending on your crystal.

[AvionicsMaster1]

Thank you. It's always nice getting a concise answer to a question. Especially when it is understandable and works.

Now if I could learn to be more concise asking the questions.

Regards.

[Darrel Taylor]

Sometimes, it's only after you've gone through the pain, that an answer makes sense.

Thanks for the original effort.