1Hz pulse generator using AT89C51

[semiconductor]

best 1 hz generator -555

I’m new to 89AT51 and programming it. I’m now trying to write a program in assembly to output a 1Hz pulse at P1.0 using Timer 0 (16-bit counter mode)
Can some one help me!

Thank you in advance!

 

[vkchau]

asm counter down at89c51

Assume fosc = 12 MHz, 1 machine cycle = 1 us
=> 1s = 1.000.000us = 50000us x 20
Here is source:
MOV TMOD, #01H ; timer 0 mode 1
LOOP:
MOV TH0, #HIGH(-50000) ; count down 50000
MOV TL0, #LOW(-50000)
SETB TR0 ; timer 0 run
JNB TF0, $ ; wait timer 0 overflow
CLR TR0 ; stop timer 0
CLR TF0 ; clear timer 0 flag
CPL P1.0 ; pulse
JMP LOOP

 

[Ajay]

timer 0 1hz

If you really want to be a fanatic for accuracy, then remember that the actual on time (and off time) in the code suggested by vkchau will be 50,000 us + the time it takes to execute the interrupt! For a 1 second pulse, this may be trivial but would be a problem if you needed, say a 1 ms pulse.

You can adjust the reload values (for example 50,007 in stead of 50,000 in this case) by knowing the ISR time.

Ajay

 

[semiconductor]

timer 0 1hz

First of all, I would like to send my best thank to all of you who have helped me!

Yeah, I do not want an accurate 1 Hz pulse. So the program vkchau posted here is to what extent useful to me. But exactly, your program just output a 10Hz pulse instead of 1 Hz pulse as indicated before (50.000 * 2, not 50.000 *20) so I have to modify a little bit, as follow:

(I use ASM51 to assembly this file)

$mod51
ORG 0000H
AJMP Start
Init:
MOV TMOD,#01H
CLR RS0
CLR RS1
Ret
Delay:
MOV R0,#20 ; count number
LOOP:
MOV TH0,#3CH ; High byte of -50.000
MOV TL0,#0B0H ; Low byte of -50.000
SETB TR0 ; Start timer
WAIT: JNB TF0,WAIT ; delay 50.000 us
CLR TR0 ;Stop Timer
CLR TF0 ;clear timer flag
DEC R0 ; decrease the count number by 1
CJNE R0,#0,Loop; if the content of register R0 is not equal to 0 then
; repeat Loop
Ret
Start:
acall Init
repeat:
CPL P1.0
Acall Delay
Ajmp Repeat
End

Of course, this program does not produce the accurate 1Hz, but is nearly 1Hz.

Lastly, Thank you to all!