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 ?


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