how to start timer in 89C51 by programing and stop by external hardware

[ZOBI]

i want to start a timer in 89c51 after a 10 usec pulse is given by pin p1.1 then timer wil continue to count the time and stop when it gets low on pin p1.2 , basicaly pin p1.2 is initialy LOW i want to stop the timer when it goes from low to HIGH and then again low after that i want to stop the timer and also i want to use that TIMER value for further process

plz can any buddy help me out for the source code of that

thanks in advance

[romel emperado]

there are many projects here using timers… go and search for that and also read this

 

http://www.8052.com/tuttimer.phtml

[ZOBI]

basically i want this in my program

 

i want to use 16 bit timer then these steps in my prog.

 

1. pin p1.0 gives high for 10 microsecond then goes LOw, on its falling edge Timer 0 starts to count UP(with the help of INT0 timer start)

 

2. Then Timer will be stopped when pin P1.1 goes from high-to-LOW means on its falling edge(with the help of INT1 timer stop)

 

3. Then the TIMER value at which timer is stop ,will be save on Accumulator “A” or any register

 

4. then i will use that value for to compare between a range of diffrent values , the prog. will check whether the value is in between

166 microsecond to 1660 microsecond         volt 1

1661 microsecond to 3320 microsecond         volt 2

3321 microsecond to 4980 microsecond         volt 3

4981 microsecond to 6640 microsecond         volt 4

                               .                                           

                               .

                               .

                               .

                               .

                               .

                               .

                               .

 

5. Then after a series of comparing/checking TIMEr value from these RANGES ,when TIMEr value comes in these any of range microcontroller will send a CODE to DAC0808 to produce a voltage of respective code like on volt 1 it will send a code to DAC0808 to produce more voltage and on sending a code of volt 2 it will send a code to DAC0808 to produce less voltage as copmared to volt and and so on..

basically i m designing a project Using ultrasonic range finder SRF04,89C51 ,DAC0808

when any object will come in front of sensor it will reflect back a the ultrasound waves which wass emited by sensor on reciving that a pin goes from high to LOw after that controller will calculate the time how much time does the wave has taken in air then it will give code to DAC0808 to produce voltages which will vibrate a motor according to the distance

here is the code which I have made to which makes pin p1.0 high for 10 usec ,start stop the timer 0 and then the VALUE of timer  TL0 & TH0 will be added and will be saved in “A” but I don’t know is this correct or not.plz chek it

org 0000h

ljmp main

ORG 0003H

setb tr0

ORG 0013H

clr a

mov r4,tl0

mov a,th0

add a,r4

ORG 0030H

MAIN:

setb tcon.3

setb tcon.1

mov Ie,#10000101b

mov tmod,#10011001b

mov tl0,#0000

mov th0,#0000

setb p1.0

call delay

delay:

l1:mov r0,#1

djnz r0,l1

nop

nop

clr p1.0

end

 

 

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