how to start timer by software and stop by external hardware and then taking resultant value of time?

[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

[Anonymous]

yaa it is very easy just check the count down timer project in 8051 microcontroller tab here at engineers garage

and you can achieve this thing by using timer interrupt, external interrupt of controller but you have to set the priority bits in interrupt priority table.

[ZOBI]

i hav read a lot about how timers ,interupts  are enabled or start and stoped

 

but i cant understand that is there possible to load DECIMAL values in counter 0?

 

like

 

mov TL0,#0000
mov TH0,#0000

 

 

[dagakshay]

hi zobi 

try this it migh work out

 

 

mov TL0,<decimal value>

 

no need of pond”#” sign or to right ‘h’ at the end….

note: max value can go to 255 since TL0 is a 8 bit register

just let me know if it works???

[ZOBI]

ok i will chek it out

 

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

 

 

[ZOBI]

i m makeing a project for blind person navigation
When any obstacle come in front of Ultrasonic range finder SRF04 ,they sends signal to 89C51 controller n  controller vibrates the vibration motors attached to any particular area where the circuit is attached so a blind can understand that he or she is close to any obstacle , n the closer the obstacle the more vibration produce, means vibration should be inversely proportional to distance between person and obstacle,

 

i hav made major part of the programing of this project but still want help from u people to tell me is this source code have some mistakes or not

 

org 0000h

ljmp main

 

ORG 0003H ; INT0 ISR

 

setb TR0 ; starts timer 0 (pin p3.2 will be connected with the pin which is giving 10 usec pulse)

 

ORG 0013H ; INT1 ISR

 

clr TRO ;stops timer 0(pin p3.3 will be connected with ECHO OUTPUT PULSE PIN of SRF04)

mov DPL,TL0             ;save the TL0 values to lower DPTR portion

mov DPH,TH0            ;save the TH0 values to upper DPTR portion

LJMp RANGE_CHECKER ;from here the DPTR value will be shifted to furhter part of this remaining programe

 

ORG 0030H 

MAIN:

setb tcon.3                     ; make INT1 edge triggerd(high-to-low) interrupt

setb tcon.1                     ;make INT0 edge triggerd(high-to-low) interrupt

mov Ie,#10000101b       ;enable external INT0,ITN1

mov tmod,#10011001b  ;make timr to strt/stop by EXTRNAL HARDWARE,MODE 1,16 bit timers

mov tl0,#0000                ;load initial values in timer TLO

mov th0,#0000                ;load initial values in timer THO

setb p1.0                        ;make pin P1.0 HIGH

call delay                        ;this delaywill  HIGH pin P1.0 for 10 usec

delay:

l1:mov r0,#1

djnz r0,l1

nop

nop

clr p1.0

end

 

 

[ZOBI]

plz tell me that is this program is correct or it needs some more addition or correction. all the details are written in front of every command after “;” sign

 

ORG 0013H                   ; INT1 ISR
clr TR0           ;stops timer 0(pin p3.3 will be connected with ECHO OUTPUT PULSE PIN of SRF04)
mov DPL,TL0                 ;save the TL0 values to lower DPTR portion
mov DPH,TH0                ;save the TH0 values to upper DPTR portion
LJMP RANGE_CHECKER ;from here the DPTR value will be shifted to furhter part of this remaining programe
RANGE_CHECKER:

 

{{{{{{here i will write further program}}}}}}

ORG 0030H
MAIN:
setb tcon.3                      ; make INT1 edge triggerd(high-to-low) interrupt
setb tcon.1                     ;make INT0 edge triggerd(high-to-low) interrupt
mov Ie,#10000101b       ;enable external INT0,ITN1
mov tmod,#10011001b  ;make timr to strt/stop by EXTRNAL HARDWARE,MODE 1,16 bit timers
mov tl0,#0000                ;load initial values in timer TLO
mov th0,#0000               ;load initial values in timer THO
setb p1.0                        ;make pin P1.0 HIGH
call delay                         ;this delay will  HIGH pin P1.0 for 10 usec
delay:
l1:mov r0,#1
djnz r0,l1
nop
nop
clr p1.0
end

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