Problem with blinking LEDs in a 89c51 circuit

[ronydc]

dear friends,

i hvae made a simple project with 89c51 and i am in trouble.
the project is --> 8 relays, 8 switches. when one wsitch is pressed, one relay becoms on and all others off.
so simple.
but the problem is --> at the start, when i firstly ON the supply, ( +5v from a regulated supply), all the LEDS blink once and goes off. after that the program works finely.
my problem is, how to remove this blinking of all the leds at the start..? is this a power supply problem..? or something needs to be dont with at the reset pin of the mcu..?( this tyme i am providing the "power on reset" to pin 9).
what modifications or additions i need to do to any microcontroller ckt to avoid this starting problem....

please advise.. friends.
-rony.

 

[aupa]

how to reset 89c51

pls, can you show the source code?

 

[IanP]

cac reset ic 89c51

Re-design your circuit (and software) in such a way that a relay (or LED) is activated when 8051's pin goes low ..
When (and this always happens) on power-on pins go high you don't need to do anything as it's their reset value (#FFh for all ports), and for you it's just inactive stage ..

Regards,
IanP

 

[nandhu015]

uln ic interface with 89c51

Use not gate. I always do it.

Regards
Nandhu

 

[ronydc]

89c51 reset

thanks friends...
the idea about using the gates or changing the software with initial high and action by making it low is really good.
your suggessions really helped me.

but,is there any solution for the circuits those are already made on pcbs and there is no scope for hardware or software changes..?
can anything done with the reset pin..? or power supply in this kind of cases..?

please discuss.
thanks.

 

[nandhu015]

Re: 89c51 reset problem

No chance at all. Once i met this prob.

Only way i found is to make small board.

Regards
Nandhu

 

[Nahian]

Re: 89c51 reset problem

not gate is really a good idea, bt to me there is a little prob on ur code.

 

[vsmGuy]

89c51 reset problem

No. This is the default behavior of ATMEL 8051. All pins are high initially and it takes significant amount of time for them to go low.

 

[sn_burki]

Re: 89c51 reset problem

it is the behaviour of ATMEL which the disadvantage concidered of Atmel, I dont know how can it be solved??? but in your case i think you should use a simple timer for all the relays before they activate, keep the timer timing in mili second.

 

[ahmedshakeel]

Re: 89c51 reset problem

hi
how r u switching on the relays,r u using some transistors to drive relays or u r using uln driver ic which is a darlington pair,as uln driver ic is open collector and outputs logic one if u give it low level on input so it might solve ur problem at reset, as output pins are high at reset
regards
Shakeel

 

[ravich_m1]

Re: 89c51 reset problem

hi

use high value of crystal osc.



ravichandran

 

[nandhu015]

Re: 89c51 reset problem

hi

use high value of crystal osc.



ravichandran

Using high value crystal osc. wont solve the prob.

Regards
Nandhu

 

[vsmGuy]

89c51 reset problem

Is it really so critical ???

Then why not use an active low circuit ??