Generåte 2 wåves of dífferent duty cycles on 2 dífferent port píns by usíng both tímers in 8051

Hello to all experts!

I want to generate two different waves on two different port pins of different duty cycle in 8051 using assembly language.

one wave is of 10 KHz of 50% duty cycle on pin p1.0
other wave is of 1 KHz of 10% duty cycle on pin p0.0

Here is the code what I get until now.

	org 0
		mov tmod, #12h          ;timer1 in mode=1 and timer0 in mode-2
		mov th0, #-50             ;reload value for timer0
		setb tr0                      ;start timer0
loop:         mov th1, #0feh
		mov tl1, #0ch
		setb tr1
wait:         jnb tf0, next                ;check if timer0 is overflowed
		clr tf0                         ;clear flag bit of timer0 is overflowed
		cpl p1.0
next:	        jnb tf1, wait                 ;chekc if timer1 is overflowed
		clr tr1                          ;stop timer1
		clr tf1                          ;clear flag bit of timer1 is overflowed
		cpl p0.0
		sjmp loop
		end

What changes should I make in order to satisfy above requirements? The above code shown is generating two different wave of 10KHz and 1KHz but both are 50% duty cycle. I want 10KHz as 50% and 1KHz as 10%.

Thank you very much

Incase of 1Khz wave, you need to check if high/low cycle has passed and accordingly You should load the timer value. for 1Khz, 1ms is your time period so for 10% duty cycle high cycle should last 0.1ms (100uS) and low time lasts for 900uS. So you need to load -100 for high time and -900 for low time.

Thank you for your reply expert.

Here is what I made changes in the above program according to your direction.

        org 0
        mov tmod, #12h       ;timer1 in mode=1 and timer0 in mode-2
        mov th0, #-50        ;reload value for timer0
        setb tr0             ;start timer0

high:   mov th1, #0ffh       ;time period for high portion of the wave
        mov tl1, #0a4h
        setb tr1

wait:   jnb tf0, next         ;check if timer0 is overflowed
        clr tf0               ;clear flag bit of timer0 is overflowed
        cpl p1.0

next:   jnb tf1, wait         ;check if timer1 is overflowed
        clr tr1                ;stop timer1
        clr tf1                ;clear flag bit of timer1 is overflowed
        cpl p0.0

low:    mov th1, #0fch        ;time for off portion of the wave
        mov tl1, #0c2h
        setb tr1
        sjmp wait
        end

This is what I tried to do. But it will not generate wave as I want because when this program enters the low label section then it will jump to wait again and then the code is moving downward from the wait. So I will not able to get wave of high portion. What should I do then?
Should I use the instruction jnb p0.0, low and jb p0.0, high just after the instruction cpl p0.0. Huh???

Keep a flag for testing high and low. When high starts set the flag high and when low starts set it low. And check it in your main loop for it.

However to get best result of this requirement. I suggest you use interrupts. You have two timers enable interrupts for both. And individual timer will do its own job in its ISR routine. Do consider it.

Keep a flag for testing high and low. When high starts set the flag high and when low starts set it low. And check it in your main loop for it.

Hello sir, I did for testing high and low. But I am not getting what do you mean by set the flag high and set the flag low. Flags are automatically set high when timers are overflowed. Isn't it sir? Am I doing something wrong?

However to get best result of this requirement. I suggest you use interrupts. You have two timers enable interrupts for both. And individual timer will do its own job in its ISR routine. Do consider it.

I know we can use interrupts. But my teacher doesn't allow me to use interrupts because we have not studied interrupts yet in the class. It will take few weeks to get this topic covered in the class. And I have to submit this topic by Wednesday (16th April, 2014). So I need urgent help and with help I want to learn too.
Kindly guide me without using interrupts.

Thank you very much sir.

Try this:

flag equ 0

    org 0
    setb flag ; start with high first
    mov tmod, #12h ;timer1 in mode=1 and timer0 in mode-2
    mov th0, #-50 ;reload value for timer0
    setb tr0 ;start timer0
 
high:
    ; check if high
    jnb flag, low
    setb flag
    mov th1, #0ffh ;time period for high portion of the wave
    mov tl1, #0a4h
    setb tr1
    sjmp wait

low:
    clr flag
    mov th1, #0fch ;time for off portion of the wave
    mov tl1, #0c2h
    setb tr1
 
wait:
    jnb tf0, next ;check if timer0 is overflowed
    clr tf0 ;clear flag bit of timer0 is overflowed
    cpl p1.0
 
next:
    jnb tf1, wait ;check if timer1 is overflowed
    clr tr1 ;stop timer1
    clr tf1 ;clear flag bit of timer1 is overflowed
    cpl p0.0
 
    sjmp high

    end

		org 0
		mov p2, #0ffh
		mov tmod, #12h
		mov th0, #-57
		setb tr0
		setb p1.0
l_ow:	mov th1, #0ffh
		mov tl1, #0a4h
		setb tr1
wait:	jnb tf0, next
		clr tf0
		cpl p1.1			;8KHz, p1.1
next:	jnb tf1, wait
		clr tr1
		clr tf1
		cpl p1.0			;1KHz, p1.0
		jnb p1.0, l_ow
		jb p1.0, h_igh
h_igh:	mov th1, #0fch
		mov tl1, #0c2h
		setb tr1
		sjmp wait
		end

Hello sir, Thank you for your reply. I need your help in this code sir. This code is generating 8KHz of clock and 1KHz of data pulses. I want to reduce 800Hz of clock and 100Hz of data pulses. What changes should I make in this code?

Thank you.

Increase the time for both the waves that should do it.

Yes, I tried to increase the time for clock but I am able to get only 4KHz minimum. I want 800Hz. If I use loop i.e. mov r0, #255 then how to use this loop sir?

I hope you have understand my thinking obviously you are experienced one.

org 0
mov p2, #0ffh
mov tmod, #12h
mov th0, #-57
mov r0, #10
mov r1, #10
setb tr0
setb p1.0

l_ow:
mov th1, #0ffh
mov tl1, #0a4h
setb tr1

wait:
jnb tf0, next
clr tf0
djnz r0, ?
cpl p1.1			;8KHz, p1.1

next:
jnb tf1, wait
clr tr1
clr tf1
djnz r1, ?
cpl p1.0			;1KHz, p1.0
jnb p1.0, l_ow
jb p1.0, h_igh

h_igh:
mov th1, #0fch
mov tl1, #0c2h
setb tr1
sjmp wait
end

Hello, This is my code. I have made changes in the program. As discussed above I want to generate 800Hz of clock (p1.1) and 100Hz of data pulses (p1.0). For this I need to create large delay. And I am confuse how to do it. I tried on my own. In capital letters are the recent changes I made. Kindly help me, what label should I use instead of "?", in order to create the delay.

Kindly help me.