8051 Microcontroller Delay Calculation Method:

This method is "invented" by "Saad Zahid" of CECOS University, when he was a student of 3rd year Electrical Engineering and it was his first time with such type of Course. He was working on this method for one week and after confirming this method's reliability with his Lecturer Engr. Mansoor Habib he submitted it and was published on
September 17, 2009.Good Job Saad.

Following is a method to calculate the delay subroutines without using timers in the Microcontroller: (Click Here to Download Pdf version for more examples)

Delay	Calculations	Code	Remarks
50mS Xtal freq =11.0592MHz	50mS/1.085uS = 46082.9
	46082.9/255 = 180.7		Its an Odd Value, so round off the result i.e. 180.7 to the nearest even number i.e 182
	46082.9 / x =182		Find value of x
	46082.9 / 253 = 182		We’ll load 253 in the inner most loop
	182 / 2 = 91		Always do this, so its result will be our outer loop
		Delay:Mov R0, #91 Here1:Mov R1, #253 Here:DJNZ R1, here DJNZ R0, here1 RET
500mS Xtal freq =11.0592MHz	500mS/1.085uS = 460829.5
	460829.5 / 255 = 1807.1		Odd number does not account as its not less than 255, innermost loop = 255
	1807.1 / 255 = 7.086		Round off to nearest higher even i.e 8
	1807.1 / x = 8
	1807.1 / 226 = 8		Inner loop = 226
	8 / 2 = 4		Outer loop = 4
		Delay:Mov R0,#4 Here2:Mov R1, #226 Here1:Mov R2, #255 Here:DJNZ R2, Here DJNZ R1, Here1 DJNZ R0,Here2 End
1Second Xtal freq= 20MHz	1 / 0.6uS = 1.6 x 10e6
	1.6 x 10e6 / 255 = 6536		Innermost loop= 255
	6536 / 255 = 25.6		Not Even so make it even i.e. 26
	6536 / x = 26
	6536 / 251 = 26		Inner loop 251
	26/2 = 13		Outer loop = 13
		Delay:Mov R0, # 13 Here2: Mov R1, # 251 Here1: Mov R2, #255 Here: DJNZ R2, Here DJNZ R1, Here1 DJNZ R0, Here2 Ret

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