Author Topic: PIC16 stupid question about powering  (Read 4067 times)

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Offline The Magic Rabbit

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PIC16 stupid question about powering
« on: September 17, 2015, 05:50:53 pm »
I've used PICs before, but only the 16F690. I've just got a sample of the 16F1789 to experiment with, and it's physically a lot larger. I also notice it has Vss and Vdd pins on both sides of the chip. Do I need to supply all 4 pins, or do I just connect whichever side is most convenient to the circuit layout? I couldn't see this covered in the data sheet. Thanks.

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Offline marshallh

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Re: PIC16 stupid question about powering
« Reply #1 on: September 17, 2015, 06:02:44 pm »
Connect all of them. This is very common on larger devices (on 672 pin fpga, you might have 200 power pins)
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Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #2 on: September 17, 2015, 06:12:32 pm »
Thanks. Presumably it's better to also have a 0.1uF capacitor for each pin rather than shared for the whole chip?

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Offline RogerRowland

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Re: PIC16 stupid question about powering
« Reply #3 on: September 17, 2015, 06:13:27 pm »
Thanks. Presumably it's better to also have a 0.1uF capacitor for each pin rather than shared for the whole chip?

Yes, bypass caps on each pair of power pins.
 

Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #4 on: September 17, 2015, 06:13:52 pm »
Awesome, thank you! :-)

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Offline Howardlong

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Re: PIC16 stupid question about powering
« Reply #5 on: September 17, 2015, 10:17:25 pm »
Roger's comments are sound. Also RA6/VCAP add a 0.1uF if you have enabled it for the internal core LDO.

This is a nice chip, it has a complicated PWM, it takes a bit to learn.

Edit: the 44 pin QFN also has AVDD and AVSS on it, you should connect and bypass those too if using that package.
« Last Edit: September 17, 2015, 10:21:24 pm by Howardlong »
 

Offline AndyC_772

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Re: PIC16 stupid question about powering
« Reply #6 on: September 18, 2015, 07:37:10 am »
Thanks. Presumably it's better to also have a 0.1uF capacitor for each pin rather than shared for the whole chip?

It's probably unnecessary to have two caps, if you have a multi-layer board with solid power and ground planes under the chip.

Provided each power pin is connected into a plane with its own via, the total inductance between the IC pin and the cap is still very low. Adding a second cap really doesn't make much difference.

Offline Howardlong

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Re: PIC16 stupid question about powering
« Reply #7 on: September 18, 2015, 07:58:01 am »
Thanks. Presumably it's better to also have a 0.1uF capacitor for each pin rather than shared for the whole chip?

It's probably unnecessary to have two caps, if you have a multi-layer board with solid power and ground planes under the chip.

Provided each power pin is connected into a plane with its own via, the total inductance between the IC pin and the cap is still very low. Adding a second cap really doesn't make much difference.

While you are almost certainly correct, and I hate the term "best practices", it is is a good rule of thumb to have decoupling of every power pin unless the data sheet recommends otherwise, and for a $0.001 part there's no harm. Certainly that's been my general practice for many decades.

If you've ever had to debug a digital board with insufficient decoupling, you'll know why, the symptoms rarely give obvious clues.
 

Offline AndyC_772

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Re: PIC16 stupid question about powering
« Reply #8 on: September 18, 2015, 08:10:23 am »
I completely agree that one decoupler per power pin is a good rule of thumb.

I think it's always worth considering what such rules are trying to achieve, and to question or modify them where appropriate, though. In this case, a PIC is a low power, low frequency device, and I believe the extra inductance of (say) 5mm distance across a plane is insignificant.

It's worth mentioning that I design a lot of very, very small PCBs, where the cost of an extra cap isn't a problem but the size most definitely can be.

The only time I've had decoupling problems with a board was one in which the stack-up was wrong. In that case it was plane-to-plane capacitance that was lacking, and no discrete components would have helped. But that's a story for another day.

Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #9 on: September 19, 2015, 09:19:20 pm »
I'm a complete newcomer to this. I'm still using strip board to do my very basic circuits. My background is computer programming, so I tend to make projects that use simple circuits and let the software make the magic happen. My last project simply involved PWM controlling some IRL520 FETs connected to strips of RGB LEDs. The next one will use more a more complex implementation and more FETs to synchronise various effects to music. I want the PWM to control the RGB mix, so I can use various processing to create the effects on the chains of 5 x R, G and B segments.

I plan to make my first etched board for this. I've got some Hydrochloric Acid, Hydrogen Peroxide, basic copper clad board, and some adhesive vinyl to use as a mask, plus obviously a means to cut it. Fingers crossed!

Everything is through-hole so chips are DIP etc. as I don't think I'm up to the challenge of soldering surface mount yet.

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Offline Xenon Photon

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Re: PIC16 stupid question about powering
« Reply #10 on: September 19, 2015, 10:18:01 pm »
My background is computer programming, so I tend to make projects that use simple circuits and let the software make the magic happen.

I suggest you start with ARM processors based micro controllers. It is almost like computer programming in C++.
 

Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #11 on: September 20, 2015, 01:00:43 am »
Are there any ARM processors that are through hole mounting and extremely cheap though? Those are the main reasons I like PIC. That and the fact I can get free samples, lol

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Offline Xenon Photon

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Re: PIC16 stupid question about powering
« Reply #12 on: September 20, 2015, 03:38:11 am »
There are few modern ARM MCUs in DIP form, for example "NXP Semiconductors LPC1114FN28/102", It is 5 US dollars on DigiKey. The best ones will be SMT parts which you can design a board for and make it breadboard compatible. An amazing board with a lot of great features like USB boot-loader is Zapta's ARM PRO MINI. This board will be good to start with because it supports C++.

I was a computer programmer mostly programming in C# and when I started dealing with MCUs I started with PICs but I kinda regretted the time I wasted on PIC when I first saw the BeagleBone. Although it is much more complicated than PICs, I found the ARM very similar to what I was doing in computer programming. I still use PICs though but not for something complicated, I prefer the ARM which makes it simpler.
« Last Edit: September 20, 2015, 03:44:56 am by Xenon Photon »
 

Offline Howardlong

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Re: PIC16 stupid question about powering
« Reply #13 on: September 20, 2015, 06:20:05 am »
I plan to make my first etched board for this. I've got some Hydrochloric Acid, Hydrogen Peroxide, basic copper clad board, and some adhesive vinyl to use as a mask, plus obviously a means to cut it. Fingers crossed!


I highly recommend either using a board house to do your PCBs or follow this advice http://www.electricstuff.co.uk/pcbs.html

By the way, I still do use stripboard, have done for forty years.
 

Offline andybarrett1

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Re: PIC16 stupid question about powering
« Reply #14 on: September 20, 2015, 07:42:55 am »

By the way, I still do use stripboard, have done for forty years.

+1  :-+
 

Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #15 on: September 20, 2015, 03:18:52 pm »
I have nothing against strip board, there's just something really appealing about making boards. Wanted to do it for years but never plucked up the courage. I already have loads of adhesive polymeric vinyls and a machine that cuts up to 600mm wide and any length with a 0.025mm accuracy, so I'd be mad not to at least try it. :-D

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Offline picandmix

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Re: PIC16 stupid question about powering
« Reply #16 on: September 20, 2015, 04:57:47 pm »
I have nothing against strip board, there's just something really appealing about making boards. Wanted to do it for years but never plucked up the courage. I already have loads of adhesive polymeric vinyls and a machine that cuts up to 600mm wide and any length with a 0.025mm accuracy, so I'd be mad not to at least try it. :-D

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Everyone has their own way of making pcbs, but  generally find making one is only worthwhile for the completed project when its ready to become the final working circuit.

Strip boards are fine for development / testing work  but do not always look that neat, though if you use these types of double sided boards they are easy to wire up and look good when finished, partic if most of the wires on the underside.
Plenty on ebay in variouus sizes but you have to search for a good price.

Pics are a good  starting point as any  imho, cheap and readily available and masses of existing help and projects on the web.

Though mentioned by others,  you have not said what you are using for progam code,   A, B, C or  Graphical ?
 

Offline The Magic Rabbit

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Re: PIC16 stupid question about powering
« Reply #17 on: September 20, 2015, 05:05:44 pm »
I've done assembler (MASM) for a few things, then just started playing with the Microchip C compiler.

Computer wise, most of my code is PHP/MySQL with XHTML on servers, or Python on the Pi these days.

I class myself as a beginner to electronics really, since I've only ever really done simple circuits with LED chains and basic heat/light sensors, and sometimes a PIC as the workhorse.

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