interrupt trouble @.1ms

[mehmetOzdemir]

i tried to get an interrupt at .1ms using dt-ints.

i used 16f877a at 4MHz and timer1 1:1 prescaler , want to toggle a led that connected to portb.7 to test interrupt.

timer1 pre-load value is 65437. The signal must be 5KHz , but it is about 2.4KHz.

The code is below.What am i missing or what is the mistake?

    INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
    INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts
    
    
    LED     VAR PORTB.7
    
    OUTPUT  LED
    
    ADCON1      = 7
    
    
    
    
    
    ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
    INT_Handler     TMR1_INT,       _TMR1_INT, PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
    ENDASM

@ INT_ENABLE  TMR1_INT     ; enable Timer 1 interrupts


    T1CON = %00000101                ; Prescaler = 1, TMR1ON

    TMR1L = $9D         ; TMR1 = 65437
    TMR1H = $FF

    
    MAIN :
    
    PAUSE 50
   
GOTO MAIN
    
    
    TMR1_INT :
    
    TMR1L = $9D
    TMR1H = $FF
    
    TOGGLE LED
@ INT_RETURN

[Charles Linquis]

When you load the timer, you have to load the High Byte first, then Low Byte.

[mehmetOzdemir]

When you load the timer, you have to load the High Byte first, then Low Byte.

thanks charles for your quick reply.

i tried to load highbyte of timer1 first , but it is not the aid.

[Acetronics2]

Hi,

You forgot to take the reload time into account ...

from MrE calc. I get 65443 ...

Why not use a 8 bits timer w/ preload = 63 ???

Alain

[mehmetOzdemir]

Hi,

Why not use a 8 bits timer w/ preload = 63 ???

Alain

i used timer0 , the problem is the same.

i used darrel taylor's intterrupt system before , but the interrupt durations was so long about 20ms there was no problem.

but when i want to use it 100 microseconds this problem occurred.

thanks for your advice.

[sayzer]

1. I would remove "PAUSE 50" from main loop.
2. To load the timer, have a word variable like timex.
For example:

TimeX VAR WORD

TimeX = 65437

TMR1L = TimeX.LowByte
TMR1H = TimeX.HighByte

3. Why not use TMR0 ?


----------------

[mehmetOzdemir]

1. I would remove "PAUSE 50" from main loop.
----------------

I CHANGED IT TO "PAUSEUS 5" THE FREQUENCY OF SIGNAL IS SAME.

3. Why not use TMR0 ?
----------------

I usually do this with tmr1 , there is not a special reason.
i used tmr0 too , but the problem is going on.

İLGİN İÇİN ÇOK TEŞEKKÜR EDERİM SAYZER.

[Bruce]

Using a PBP interrupt eats hundreds of instruction cycles just saving & restoring PBP system
variables.

You can get much more accurate timing, and save hundreds of instruction cycles with a
CCP Compare interrupt & .asm interrupt handler.

Try something like this;

  INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
  INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts
    
    LED VAR PORTB.7
    OUTPUT LED
    LED = 1    
    ADCON1 = 7 
  
    ASM
INT_LIST  macro    ; IntSource, Label,  Type, ResetFlag?
    INT_Handler     CCP1_INT,   CCP_INT, ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
    ENDASM

@ INT_ENABLE  CCP1_INT  ; enable Compare interrupt

    T1CON = %00000001   ; Prescaler = 1, TMR1ON
    CCP1CON = %00001011 ; compare mode, int when TMR1 = CCPR1
    CCPR1L = 100        ; interrupt every 100 instruction cycles
    CCPR1H = 0    
   
MAIN:
    PAUSE 50
    GOTO MAIN
    
ASM
CCP_INT
    MOVLW  0x80     ; W = %10000000
    XORWF  PORTB,F  ; toggle RB7 on each interrupt
    INT_RETURN
ENDASM

This should give you a 5kHz signal on RB7, with Timer1 reset by hardware. To change the
frequency, just change the value in CCPR1 high & low registers.

See analyzer screen capture attached.

[mehmetOzdemir]

it is realy great bruce.

I HAVE TO USE ASM INTERRUPTS AFTER THAT.

The frequency is 5KHz.

And where can i find some sample codes to use asm interrupt routines in PBP.

thank you very much..

[Bruce]

For examples of using assembler interrupts look at some of Darell Taylors code, and look
through a few of the examples on MeLabs website.