Comments on: PIC stack overflow

By: Michiel Bruijn

Michiel Bruijn — Fri, 10 Feb 2012 14:37:44 +0000

After spending too much time on debugging a stack overflow problem I like to mention an other scenario causing stack overflow , not mentioned yet in the top of this article.
In my case I reserved, as described in several articles, general purpose registers, for saving W, STATUS and PCLATH when entering interrupt subroutines(ISR). If you don’t reserve registers with the same (short) address in the other banks for this purpose then you can have stack overflow bugs as I’ve learned the hard way.
Hopefully this will help someone else with this sort of bugs.

By: David Bronke

David Bronke — Fri, 25 Nov 2011 13:22:30 +0000

I’m a hobbyist PIC developer who got his start taking a microcontrollers class in college. The class started us out with PICs, and though I’ve looked at other MCUs (mostly Atmel and ARM-based ones) over the years, I haven’t yet been able to switch.

Entry cost is a significant concern for me. With PIC, you can get a decent programmer (the PicKit2) for $35 direct from Microchip, and there’s several cheaper programmers available, including several do-it-yourself designs that can be assembled for under $10 if you have a serial port. When looking into Atmel, I initially couldn’t find anything under $100 that would get me a working programmer and software, though now I’ve found a good, cheap in-circuit debugger for their 8-bit products that only costs $34, so there do seem to be options there as well. However, I have never found a way to figure out how much an AVR MCU will cost without specifically asking Atmel for a quote (unlike Microchip, Atmel’s site doesn’t list prices), and their samples process is much more involved and restricted than Microchip’s.

Another thing that PIC does very well on is providing high-end devices in DIP packages. I recently looked at Atmel when trying to put together a parts list for a custom keyboard controller I’m building, and was disappointed to find that Atmel doesn’t actually sell any MCUs with USB support in a DIP package; anything they have that supports USB is surface-mount, which makes it impossible to use with a standard prototyping board without first attaching it to some sort of adapter. Microchip, on the other hand, sells almost 150 different models of PICs which include USB support and come in a DIP package. There are some third-party solutions available to adapt AVRs with USB support to a DIP format, such as the Teensy and Teensy++ provided by PJRC, but they’re much more expensive… the Teensy++ (which is the only model I found with enough pins to work for this project) is $24 each; the PIC I ended up choosing instead (the PIC18F4550) only costs $4.47 each.

Atmel has interested me for a long time, but given that this is only a hobby for me, I haven’t seen enough reason to spend the time and money required to switch. If I were to get the opportunity to use microcontrollers in a project at work, I would choose PIC without a second thought, since I’m more familiar with it and already own all of the tools required.

By: Nitin Sangale

Nitin Sangale — Wed, 09 Nov 2011 11:34:12 +0000

Excellent guide for embedded engineers…! Thanks for such valuable knowledge.

By: Nigel Jones

Nigel Jones — Thu, 02 Jun 2011 11:46:45 +0000

The first time I looked at PIC14 assembler (having programmed 6800′s, Z80s, AVRs etc for years) I thought it was someone’s idea of a joke! Thus I agree that if you can handle PIC14, you can probably do anything. While I agree that Microchip has made a serious commitment to keeping parts available for years (I suspect in part because they buy fully depreciated fabs), I don’t think they are alone in this regard. Notwithstanding that, future parts availability is a very serious design issue; indeed every year I do a reasonable amount of work for clients redesigning products where parts are no longer available.

Finally thank you for such a thoughtful comment. One of the things I really like about those who comment on this blog is that the comments are well reasoned and devoid of religious fervour. It’s quite refreshing compared to some of the things that get posted on other forums.

By: Wouter van Ooijen

Wouter van Ooijen — Thu, 02 Jun 2011 08:16:38 +0000

As a teacher I do a PIC assembler class. One thing I tell my students is that once they have mastered the 14-bit core PICs anything else will be a piece of cake.

More seriously, IMO the main reason PICs are so popular (beside being popular, which is a big factor) is that Microchip has a very good reputation for delivering the chips, and continuing to deliver them. If you make a product now and still want to sell it (without the hassle of re-design, re-testing, re-certification, etc) I think Microchip is the only choice. If OTOH you want a the best bang for the buck right now (and don’t care much what happens in 5 years, or don’t mind sitching to a different chip) Microchip it is definitely the wrong choice.

By: Nigel Jones

Nigel Jones — Fri, 04 Mar 2011 11:41:31 +0000

I think that’s a very important point. I do a fair amount of work for clients simply based on parts obsolescence. The fact that Microchip keeps parts around forever certainly helps maintain brand loyalty.

By: cyrile

cyrile — Fri, 04 Mar 2011 08:53:28 +0000

i almost forgot, microchip keep many pics active, the ones we used many years ago are still avaible, or a very close equivalent.
i’ts somehow interesting for us, as we are not in a race for the last product !

By: cyrile

cyrile — Fri, 04 Mar 2011 08:48:28 +0000

Hi,

I use PIC because when i was a student, i got an old programmer. then i had many sample of their circuits, free. it was a criteras for me, having them free cause it’s a little bit expensive for a student without money.

I meet your point, i agree. architecture is awfull, the two interrupts vectors are not sufficient for effective programming, sometimes it’s a nigthmare… small stack, really small.
some bugs in the compiler also..

But the computing power is sufficient for me, and when i need more power, i have my own DSP board.

Maybe i’ll change for ARM one day..

By: Henrique

Henrique — Mon, 24 Jan 2011 17:43:05 +0000

It’s simple, every time you want a microcontroller to do some dumb & quick job, you ask your colleagues about witch mcu you should choose.. the answers are:
- “Use a ARM MCU! I’ve seen some pretty cheap around, or maybe you should buy a kit”
- “Use AVR! I’ve never used one but some people say they are very easy to deal with, just don’t know which to buy.”
- “Use 8051! But do it in assembly. 8051 compilers are lame”

An then you hear:
- “Use PIC. I’ve dealt with them.. in fact i have a programmer in my house”
- “Hey! but I have a programmer in my office.. give me just a minute..”
- “Well, I have half your code written with test cases and everything!”
- “You know what? let me just do that with you and by the end of the day will have it ready!”

and so it goes…

By: Horsedorf

Horsedorf — Wed, 15 Dec 2010 18:09:08 +0000

Something that one of the financiers that sat on the board of directors at Netapp said to the senior executive staff of Netapp comes to mind. “When are you engineers going to get that it doesn’t have to be perfect, it just has to be good enough.” And that, is where the Pic sits.. It’s not perfect, but it *IS* “good enough”.