Re : 16f84 and Led with multisim.

[lacy]

Joris D. I sent an e-mail to you through the support address you had in your last post. Sorry about that but I overlooked it when reading your post. Now everything is procedurally correct.

[Joris_D.]

Hi,

I suppose you went to www.ni.com/support and filed a question true that webpage. Thats just perfect. Really nice that you did it that way. Only problem with that is that we have support departments over the whole world and i guess you're not Belgian. So probably you're question went to the support team in the country that is connected to your forum profiel "lacy". Those people normally will also be able to help you perfectly and maybe even better. If you still need my help, just let me know and i'll mail to you with my own e-mail adress.

[lacy]

I didn't realize you from a different country. I keep forgetting that Multisim is international as well as this forum. I will wait and see what response I get from them here in the U.S. If  they don't  understand what I am getting at in that e-mail then I will get back with you and see what you can make of it since you are familiar with what we are discussing.

Thanks for you help and I will get back with you if it is necessary.

[tweetysat]

Hello lacy and Joris.
Thanks for trying to help me.
Joris, I tried downloading your zip file but it seems to be corrupted.  So i cannot try your code.
I looked in mine but the pullup resistance is active.  I also tried to desactivate it but with same results.
I'm waiting for your code to see the difference with mine.

[lacy]

Hi there tweetysat.

It has really nothing to do with your code. It would work with your code as is, but you need to tie a resistor of 600 ohms from VCC to the junction of  the LED Anode and the port pin. This is what he done. The only code change he made was in order to used a port pin as an input and tie a switch to it to turn the LED on or off. 

PortA does not have pull-up resistors so one must be tied in to provide the power necessary to activate the LED. PortB on the other hand does have pullup resistors already there and nothing else is require to make use of them. It would seem to me that PortA was inteded to be used for input while PortB was intended for use as output even though they can be used for either. This is the way I see it and I have been known to be wrong on occasion.

Let me know if any further assistance is required and I will see what I can do.

[Joris_D.]

Hi,

Lacy's explination is completely right. So I don't have much to add. But I will add the files once more (rename led.txt to led.asm, forum won't take .asm).
I hope they work now perhaps the problem lies in the fact that i'm using multisim 10? Let me know if i need to save it for another version.
Take a look at the circuit file. Here you will see the pull up resistor i used. And examine the asm file i have made minor changes to the code.
But if i remember correctly yours was not to bad either. Keep me posted.

[tweetysat]

Hello Joris.
It's very kind to take some of your time to help me.
Are you sure it's the right circuit file ?  I've downloaded it but it's exactly the same as mine.  I don't see the pull-up resistor.
In the same time i tried to modify it to add the resistor.
So i have:
RA2 -- led -- 0v
and
5v -- 600ohm -- junction between RA2 and led.
It's right ?
I tried and ... it works.
But I still not understand why it's not working without this pull-up resistor.  The same circuit (without pull-up)  and code are working 'in real-life' and in proteus.
ps : I'm also using multisim 10 (10.0.343).

[Joris_D.]

Hi,

Yeah i'm sorry. I think i took the wrong files from my pc. I'm gonna take some time to search them. In the mean time, try to have a +5V connected with resistor 330 ohm or something, in series with led and to ground and then connect your pin from the PIC in between the resistor and the led. This should do the trick. I'll get back to you when i find the files or i'll make them again.

[Joris_D.]

Hi,

Here you go, didn't found them so i made a new example based on your code. The circuit works with a switch to let you see the control.
And the code also has PORTA put on output for everything besides PORTA,1. This is the input for the switch. Try it out and let me know what you think.

[lacy]

Hi Joris D.

I think I understand what he is getting at here. Apparently he has built his original circuit and it worked without the pull-up resistor on the LED. Also he has tried the same circuit and code in Proteus and it works without the resistor. So one of 2 things is happening: Either both the real circuit and Proteus are giving the wrong results or Multisim 10 is giving the wrong results.

I believe this to be what he is asking at this point. Since I haven't built the circut nor do I have Proteus I can not comment on what is actually taking place here. It is worth investigating, because if Multisim is somehow incorrect in its results then that will have to be put on the fix list.