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Time delay for 8086

Posted on 2003-12-05
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Last Modified: 2006-11-17
I am writting an assembly program for 8086.I need to have a time delay which must be 1 sec.I thought something like that:

AGAIN2:  MOV DI,01ADH
AGAIN:    MOV BP,FFFFH
              NOP   ;(3 CYCLES)
              NOP   ;(3 CYCLES)
              NOP   ;(3 CYCLES)
              DEC BP  ;(2 CYCLES)
              JNZ AGAIN   ;(i am assuming it is 5 CYCLES)
              DEC DI
              JNZ AGAIN  


Is that code right?Will it be a delay of a second?

Is there any way to make this delay using the RTC clock of my PC?
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2 Comments
 
LVL 11

Accepted Solution

by:
dimitry earned 500 total points
ID: 9883531
It can be delay of one second. Maybe less, maybe more. It depends on your CPU speed.
The proper way is to read clock tickes with the help of INT 1Ah:
  MOV AH, 0
  INT 1Ah
  CX <- High clock word
  DX <- Low clock word
  For a second you need to count ~ 18 ticks

So code can be something like this:
  MOV DI, 18
  MOV AH, 0
  INT 1Ah
  MOV BX, DX
Delay:
  MOV AH, 0
  INT 1Ah
  SUB DX, BX
  CMP DI, DX
  JA Delay

Note: You need to think about the case when "first" DX will be bigger than new one...
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LVL 37

Expert Comment

by:bbao
ID: 9893127
yes, the right way to make delay is programing with RTC. see here for complete guide and source code in assembly:

http://cs.smith.edu/~thiebaut/ArtOfAssembly/CH10/CH10-5.html

hope it helps,
bbao
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