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Programming the Timer 8253

Posted on 1997-08-21
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Last Modified: 2008-03-10
I want to know how to program the 8253 timer on port 40h-43h. So that I can implement this to the joystick reading procedures, use it as a delay... Everywhere where the timing or delays are needed
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Question by:Kasumi
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Accepted Solution

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alona041797 earned 150 total points
ID: 1215444
You should write an interrupt handler for interrupt 8 as following:

Uses Dos {,...};

var defint8:procedure;
   
procedure myint8; interrupt;
  begin
    {Whatever you need to be run 18.2 times per second}
    inline($9C);
    defint8;
  end;

{...}

begin {Main Program}
  {...}
  getintvec(8,@defint8);
  setintvec(8,@myint8);
  {...Most of your program here...}
  setintvec(8,@defint8);
end. {Main Program}

{Hope this helps...}
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Author Comment

by:Kasumi
ID: 1215445
Well this isn't that hard for me to figure uot by myslef. But I wanted to know HOW to write the handler for it. I mean I want to replace the interrup by my own function.
I don't want to call the int at all.
So let's say that one of the things the interrupthas to do, is increasing the time counter on 0000h:046ch.
So I want to know how to do this.
My guess:
mov dx,40h
insd eax,dx
xor bx,bx
mov es,bx
mov edi,046ch
mov dword ptr es:[edi],eax
I want mz function to replace the int. It desn't need to have EVERYTHING the timerinterrupt has, but the basic functions should be included.

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Expert Comment

by:alona041797
ID: 1215446
Why should you replace the original handler?
The assembler code you wrote will correctly update the timer, which is the most important thing the hardware interrupt does.
BUT, If you intend to write your own handler you must acknowledge the interrupt by:
  port[$20]:=$20;
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Author Comment

by:Kasumi
ID: 1215447
Ok. I hate interrupts. They are too slow. And it's a problem in Protected Mode always to warp the int into the 31h.
I want to know, how to use the ports. The ports for the timer
are 40h-43h but I don't know, what info in each port is. Thats what I want to have. A kind of documentation.
So that I know, what I have in each port, how can I set it etc.

Bye


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Author Comment

by:Kasumi
ID: 1215448
I forgot:
$Why the port[$20]=$20??
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Expert Comment

by:alona041797
ID: 1215449
I have exact docmentation of the ports of the 8253, but to use it you MUST use interrupts! The 8253 channel 0 generates int 8, channel 1 refreshes the DRAM and channel 2 is for the PC speaker... you *can* start it counting and check its value by using channel 2. Please post your e-mail address or send it to me <alon.a@usa.net> for that file.
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Expert Comment

by:alona041797
ID: 1215450
The port[$20]:=$20 tells the hardware interrupt manager that the hardware interrupt has been acknowledged, so it can send more hardware interrupts of the smae kind.
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