View Full Version : Quick question regarding Pic selection
lew247
- 27th April 2010, 13:38
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
- 27th April 2010, 14:05
Give this a try.
http://www.picbasic.co.uk/forum/content.php?r=103-Microchip-Product-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
- 27th April 2010, 16:31
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
- 27th April 2010, 16:45
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 ICSPDATCorrect!
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
- 27th April 2010, 18:01
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/content.php?r=105-SMD-Prototyping
circuitpro
- 27th April 2010, 18:53
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
- 27th April 2010, 23:18
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
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