PIC 12 and 14 bits instruction sets

[Joel Rainville]

Since I started playing with PICs, I have assumed that the 12 bit instruction set was limited to the PIC10, while the PIC12 and PIC16 used the 14 bit instruction set.

Now it appears that the **broken link removed**/**broken link removed**/**broken link removed** family is using the the 12 bit instruction set. When I first saw this on the 16F505 product page, which is not yet in production, I thought "oh, there's a typo". Well, it's not, the datasheet clearly states 12 bit instruction set.

While I can see the need for a smaller instruction set in cheaper packages, I am left wondering why call them PIC12s and PIC16 when they actually look like they're just PIC10s with more pins? Not to mention that they are completely software incompatible with other PIC12s and PIC16s? Are there other examples of PIC12s and PIC16s using the 12 bit instruction set? Maybe some older OTP ones?

 

[Joel Rainville]

Ok, I'm going to answer my own post here

It looks like they just don't want to change their marketing strategies for their smaller microcontrollers. They make a big deal about the PIC10 being 6 pins microcontrollers, so they probably wanna keep it that way.

Also, all PIC12s are 8 pins. So classifying the 508 & 509 as PIC12s and the 505 as a 14 pins PIC16 is consistant pin count classification. And they actually all are much more powerful than PIC10s. They just happen to share the same small instruction set.

I guess what surprised and confused me is the fact that Microchip doesn't seem to make a big fuss about the adoption of the 12 bit set for the bigger PICs, when I thought they should/would/could :lol:

 

[Jay.slovak]

The difference between 12 and 14 bit program word is not great. Seems like Stack is limited to 2 levels, no interrupts are available and you can't load TRIS and OPTION registers dirrectly, not a big deal. But I preffer to stick to 14 and 16 bits (and the only PIC that I work with that has 12bit is the 10F20x).
The reason for 16Fs with 12bit program word is to provide a very cheap and simple MCU (with more I/Os), sometimes every cent counts.
Also some 16C PICs used to be 12bit (16C55 I guess) so they make new PICs that are compatible with the old ones.

 

[Joel Rainville]

Yeah, you're right, there are a few 16Cs using the 12 bit set.

I think what originally confused me is that Microchip sometimes refers to the 14 bit instruction set as the PIC16 instruction set. But I assumed there were more differences between the two sets, which are in fact very similar, so it doesn't really matter. Not to hobbyists at least, but more to industries for whom, like you said, every cent counts.

 

[Nigel Goodwin]

Yeah, you're right, there are a few 16Cs using the 12 bit set.

I think what originally confused me is that Microchip sometimes refers to the 14 bit instruction set as the PIC16 instruction set. But I assumed there were more differences between the two sets, which are in fact very similar, so it doesn't really matter. Not to hobbyists at least, but more to industries for whom, like you said, every cent counts.

Your confusion arises because you've come to PIC very late, your mention of 10 series and 12 series 14 bit shows that.

In 'general' 12 series were 12 bit, and 16 series were 12 or 14 bit (the older ones being 12 bit). But in much later production a small number of 14 bit 12 series have been produced - basically just 16F series chips in a smaller package.

The numbers don't refer to the number of bits anyway, just to low range, mid range, and top range - but this has become confused by the later chips released.