How can pic16f84a blink a led without external oscillator

[AriHell]

internal oscillator?

Can pic16f84a blink a led without an external oscillator or control a lcd without one?
How can i do that if that is possible?

Thank You.

 

[wp100]

Re: internal oscillator?

Hi,

That chip does not have an internal oscillator, so you must use an external crystal or RC.

 

[AriHell]

Re: internal oscillator?

thank you for your answer.

what kind of Quartz Crystal Resonator i need to use? 4Mhz or it doesnt matter?

 

[wp100]

Re: internal oscillator?

Hi,

The crystal determines how fast the micro runs - on the 84A you can use almost anything from 32k hz up to 10 meg hz.
A 4meg hz crystal with 2 x 22pf capactitors is a good starting point - see the data sheet for details.

The 16F84A is a very old chip, there are loads of better ones to use with internal oscillators etc - any reason you have to use that chip ?

 

[pranam77]

internal oscillator?

If you wanna blink a LED with internal oscillator, you may use PIC16F628A which is PIN compatible with the one you are using. But the code written for F84 needs to be modified to be used with F628A. Good luck

 

[AriHell]

Re: internal oscillator?

I will probably order 4Mhz crystal, but right now i have 8.579545MHz 3.579545MHz 4.433619MHz will it work with one of them?

 

[pranam77]

internal oscillator?

Yes it will work with any of them. Only thing you notice is the blinking speed rises with the oscillator frequency as already mentioned by "wp100". Good luck

 

[AriHell]

internal oscillator?

last thing i need to know... what kind of cap i need to use and how many pf it should be?
(i notice that people use 22pf)
can i use 1uf instead?

 

[wp100]

Re: internal oscillator?

Hi,

No, you must use the 22pf caps as specified in the chips datasheet - oscillator section.
You can use the next nearest value eg 15pf or 27pf but anything else much larger and it will not oscillate properly so your pic will do nothing.

 

[AriHell]

internal oscillator?

it is a Ceramic Capacitor right?

 

[embeddedlover]

Re: internal oscillator?

ya it is ceramic capacitor
the capacitor u have to use for a particular frequency will be mentioned by the crystal datasheet
if ur crystal frequency is critical factor use the mentioned caps
the caps that u have to use determines the resonant frequency of the crystal, a deviation from the required value doesn't produce the intended frequency
u can have a look at the below doc for info on crystal oscillators

 

[wp100]

Re: internal oscillator?

Hi Arihell,

Your oscillator questions imply you are rather new to the Pic micro side of things.

Did make me wonder how the rest of your led circuit and programming of the 84A chip will be done.
All the members on the forum will help steer you in the right direction if you are unsure of things; also there are quite a few recommended beginners Pic tutorials out there which cover both hardware and software.

This is a good one although the programmer used is rather old by todays standards and there are better alternatives.
http://www.winpicprog.co.uk/pic_tutorial.htm