interrupt trouble @.1ms

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?

Code:

---

    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

---

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

Quote:

---

Originally Posted by Charles Linquis

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.

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

Quote:

---

Originally Posted by Acetronics

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.

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

Code:

---

TimeX VAR WORD

TimeX = 65437

TMR1L = TimeX.LowByte
TMR1H = TimeX.HighByte

---

3. Why not use TMR0 ?


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

Quote:

---

Originally Posted by sayzer

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

---

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

Quote:

---

Originally Posted by sayzer

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.

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;

Code:

---

  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.

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..

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