pic hardware question for a newbe

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Ricardoco

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Before i decide to learn yet another language i have a few questions on the hardware, i hope that someone will find the time to help me, i have been given about 150 16F84's so after them living in my workshop for a while i have decided to see what they are all about, i have been looking at example circuits and was wondering if each chip in a circuit had to have its own 4mhz crystal oscilator or if more than one chip could be connected to it, i realise that there are other chips out there with built in oscilators but i have these chips and it seems a shame to waste them, also at what voltage do the respective inputs on the chips (eg: RA0) go high and is this the same to pull it low, and last but not least (dont forget im new and keen) do you know where there are any examples of basic timer programs that range from 10s to 2hrs as i have only seen very short timers in the example circuits i have seen, thankyou.
 

All the answers to these questions are in the 16F84 datasheet, you should download it and read it.

But, basically, yes you can use just one oscillator (it's described in the datasheet), and the inputs are basically standard CMOS logic, although there is at least one which has a schmitt trigger input - again the datasheet explains it.

and last but not least (dont forget im new and keen) do you know where there are any examples of basic timer programs that range from 10s to 2hrs as i have only seen very short timers in the example circuits i have seen, thankyou.
Click to expand...

It's just a question of scaling up, adding more registers to the counting registers.
 
Ricardoco said:
i have been looking at example circuits and was wondering if each chip in a circuit had to have its own 4mhz crystal oscilator or if more than one chip could be connected to it
Click to expand...

An oscillator and a crystal are two different things. An external oscillator can drive more than one chip, but how many chips depends on the oscillator and to some degree trace length. A crystal probably couldn't drive more than one chip, but who knows? Anyways they're cheap so I wouldn't even bother trying it.
 

Someone else who hasn't looked at the datasheet :lol:

It shows you EXACTLY how to do it!.
 
It was always my thought that while you can use an oscillator for multiple PICs, you could only use one crystal per PIC.

The datasheet has the PIC using a dual inverter feedback loop for use with a crystal. Are you saying that the inversion loops from multiple PICs won't play havoc with each other, trying to resonate a single crystal? Everything should work fine?

It's not that I haven't looked at the datasheet. I have many times. It just isn't clear to me. I also couldn't find in the datasheet exactly how to connect multiple PICs to the same crystal. I saw many diagrams dealing with connecting one to one. I don't even see multiples mentioned. :?
 
Ahhhh i now see the light

Correct me if i am wrong but the section you are refering to in the data sheet is 8-5 titled: external parallel resonant crystal oscillator circuit making use of two 74AS04 inverters and a 10k pot for bias this circuit can also be found on the world wide web @ z80.info/uexosc.htm thankyou very much for showing me the error of not reading the data sheet, to answer the other chaps question, it is not a case of cost it is a case of space but thanks for you input anyhow
 
Re: Ahhhh i now see the light


Please accept my apologies, I can no longer find it in a quick search of the current datasheets - it must have been in an old datasheet.

Anyway, there are two oscillator connections for a crystal, an input, and an output. One PIC has a crystal and two capacitors connected as normal, but the oscillator output of this PIC also connects to the oscillator input of the second PIC - so the oscillator output of the first PIC becomes an external oscillator for the second one.
 
hmmmmmmmmmm

Nigel Goodwin Wrote:

Thanks Nigel, its not gone un-noticed how helpfull you are, I appreciate it a lot. With reference to yr reply above, Does the osc output from the ic have the same frequency as the input, its may seem a silly question but i thought i remember reading somewhere that the output frequency is half the input frequency, and do you know where there is a sample diagram i can look at please ...its probably me getting things mixed up but i am serios about learning this and i want to get the hardware side clear in my mind so im not trying to work that out as well when i am doing the programming thankyou for the time From Rick (ps how do i get rid of the word quote at the top there??)
 
Re: hmmmmmmmmmm


The PIC runs internally at 1/4 of the external clock speed, most processors do this - many run considerably less than 1/4!.

The oscillator output to the crystal runs at the crystal frequency.


You could try searching the MicroChip application notes, I've certainly seen it somewhere - I think it was on an old datasheet.

BTW, why are you wanting to run multiple PIC's?.

To get rid of the word 'quote' you can simply delete it, but you need to make sure they have a matching '/quote'. You mustn't leave an odd 'quote' or '/quote' in the text.
 
Reply

Hi Nigel i hope you dont mind but i have PM'd You with the reply to your question By the way 2nd Dan! blimey i would think that is a great way to shake the cobwebs out, judging by your 1988 pictures.. thanks From Rick
 
Re: Reply

Ricardoco said:
Hi Nigel i hope you dont mind but i have PM'd You with the reply to your question By the way 2nd Dan! blimey i would think that is a great way to shake the cobwebs out, judging by your 1988 pictures.. thanks From Rick
Click to expand...

I was due to take my 3rd Dan about two weeks ago, but I've not trained for about two years (bad knees!) - I only teach now.

As long as I don't train hard (as you have to for a grading!) my knees are fine, but a good 'session' leaves me in pain for a number of weeks - I'd sooner not bother :lol:
 
hey Nigel u are 2nd Dan. wow!!!!

my father is also a 2nd Dan and he also used to teach martial arts.

im also interested in martial arts but im too skinny :lol:

anyway, Ricardoco where did u get 150 16F84's from?? just curious.

you might like reading the EPE Pic Tutorial which is based on the 16F84

EDIT

EPE PIC Tutorial V2 – PART 1
**broken link removed**

EPE PIC Tutorial V2 – PART 2
**broken link removed**

EPE PIC Tutorial V2 – PART 3
**broken link removed**
 
Re: hmmmmm

samcheetah said:
Ricardoco where did u get 150 16F84's from?? just curious.
Click to expand...

My father was an Aerospace Prototyping Engineer (taken me years to give up trying to fight the genes :roll: ) he has now given me 40 years of junk although its not junk to me its a new world

Nigel Goodwin said:
As long as I don't train hard (as you have to for a grading!) my knees are fine, but a good 'session' leaves me in pain for a number of weeks - I'd sooner not bother
Click to expand...

Hmmmm you are not the first person i know to do the martial arts and have bad knees, tell me is it an activity that damages your knees (i was under the impression that it was an activity that was designed around the bodies natural movement patterns without strain, or is it your past that has dameged your knees, maybe started a bit late


AAh before i go where do you get your parts from as maplin is dying a death lately ie: Zif sockets and 40 pin PIC's and the like .[/quote][/quote]
 
Re: hmmmmm


They didn't go doing martial arts (it was actually carrying a cup of tea at work!), Ju Jitsu isn't bad on joints, that was karate, back in the old days when they were doing full power punches and kicks into free air. This rapidly damages the joints, many of the top men from the 70's are now fairly well crippled :cry:
 
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