Quick question regarding Pic selection

[lew247]

I'm trying to get back into programming and making a board up, but after having brain surgery it's very hard to remember certain things such as the simplest items.


Can anyone tell me what would be a good pic to use for the following?

I need 16 I/O pins
Plus the programming pins obviously (unless they can be used a i/o pins and also programming pins, not cure on that I can't remember if it's possibly or not, or easy or not
Program memory of just under 8k

as few pins as possible to achieve the above, ie no 40 pin package like the 16f887 as it's physically too big.

I did consider an smd version but honestly don't know if I could solder it in place.

[mackrackit]

Give this a try.
http://www.picbasic.co.uk/forum/cont...-Selector-Tool

You can use the programming pins for I/O, You may have to isolate them during programming.

Try to find one that can be set for MCLRE as an input, but again isolate at program time.

Do you need ADC, Hardware serial, etc?

[lew247]

Thanks for that just what I needed

No special pins needed, it's all going to be normal i/o pins

Basically a fancy switch with temp sensing to control the switching

I've decided to allow for any possibilities I may have in the future and use a 16f887 44 pin Probably qfn 44 package

I know I'm going to have problems soldering onto this, but I'll figure it out

One question though as I cant figure this out (yet) I've got a pickit 2 programmer somewhere in the place, and will probably use that and I'll put a header on the board so it literally plugs in

I've got so far the MCLR pin 18 goes to +5v via a resistor around 20k
Vss and Vdd pins are obvious

its the actual programming pins I'm uncertain of

I was going to use
pins 16 RB6 ICSPCLK
& Pin 17 RB7 ICSPDAT

Then I noticed pin 12 RB3 is PGM - will this be a problem, or what does it do? or can I ignore this if I'm using pin 12 as an I/O pin


There will be an lcd connected to pins RB0 - RB5


Sorry for such basic and what probably sounds stupid questions, I've read the datasheet but it's just going through my head, not going into it.

[mackrackit]

The cool thing about the 887 is the MCLR pin can be made an input, then it does not need to be connected to anything but the programmer if you are not using it for an input.

I was going to use
pins 16 RB6 ICSPCLK
& Pin 17 RB7 ICSPDAT

Correct!

The PGM if configured for this is for low-voltage programming. You probably will not be doing that so the pin can be used for a "normal" I/O.

Sorry for such basic and what probably sounds stupid questions, I've read the datasheet but it's just going through my head, not going into it.

No problems with asking questions, that is what the forum is for.

[mackrackit]

I've decided to allow for any possibilities I may have in the future and use a 16f887 44 pin Probably qfn 44 package

I know I'm going to have problems soldering onto this, but I'll figure it out

This may or may not help.
http://www.picbasic.co.uk/forum/cont...MD-Prototyping

[circuitpro]

I have been using this to help with part selection lately, and find it a big help. Give it a try:

http://www.microchip.com/maps/Search2.aspx

[Byte_Butcher]

I've decided to allow for any possibilities I may have in the future and use a 16f887 44 pin Probably qfn 44 package

I know I'm going to have problems soldering onto this, but I'll figure it out

If you use a QFN package you WILL have trouble soldering it unless you use a reflow oven or hotplate. The QFN package has no exposed leads. Just pads underneath the chip.

Unless you have some particular reason for the QFN package, I might recommend the TQFP package instead. That has leads you can actually see and solder if you have a little skill and a good iron. A reflow oven is still easier though...


Steve