Simple PIC Question

[Marlowe]

and maybe also a stupid question too ... what is the difference between a
PIC
chip (such as a 16F84) and the "A" version (such as a 16F84A) of that same
chip???

 

[Dave Platt]

and maybe also a stupid question too ... what is the difference between a

PIC
chip (such as a 16F84) and the "A" version (such as a 16F84A) of that same
chip???

To find out in detail, you would have to compare the two data sheets.

In general, I believe that the "A" revisions of the parts use an
updated silicon fabrication process, and/or a smaller die, and/or have
some bug fixes in their design. There are sometimes differences in
the types or speeds of external crystal that they can use, or the
amount of current they can source/sink into their pins.

It's not uncommon for Microchip to continue to continue to produce the
original version of a chip, for years after the newer version is in
full production. The older version is often somewhat more expensive,
and the data sheet often says "Not recommended for new designs, use
the PICxxxxA instead".

I'd guess that they produce the older versions because some customers
have designs which [1] were dependent on quirks of the older version,
or [2] were qualified for manufacturing with the older version, and
would require a lengthy and expensive re-qualification (to e.g.
military or medical specifications) if they change to using a newer
"almost-equivalent-and-mostly-better" version.

 

[Michael A. Covington]

and maybe also a stupid question too ... what is the difference between a
PIC
chip (such as a 16F84) and the "A" version (such as a 16F84A) of that same
chip???

The manufacturer's data sheets (www.microchip.com) will tell you.

As I recall, the assembly language of those two is the same, but the actual
assembled code is slightly different -- the .hex and binary files aren't
interchangeable.

 

[Roger Hamlett]

and maybe also a stupid question too ... what is the difference between a
PIC
chip (such as a 16F84) and the "A" version (such as a 16F84A) of that same
chip???

It varies.
Originally, the 'A' variants were latter, usually faster versions of the
same chips. However some of the more recent 'A' variants, have had as many
differences to the normal version, as other chips using a dfferent
number!. So (for instance), the 16F876A, has the comparator module
present, and differences in it's programming algorithm compared to the
16F876...
In the case of the 84, the original chip was the 16C84, which was flash
programmable, yet used the 'C' designator. Then this had the RAM doubled,
and was sold as the F84. Then the F84A, pushed the clock rate from 10MHz
to 20MHz. In each of these 'steps', the chips were (largely) reverse
compatible, with the F84A, still able to run code written for the C84.
This is not true of the F876A, where the extra initialisation to turn off
the comparator is needed to use F876 code.
The only answer is to read the individual data sheets. If the latter sheet
is a single sheet listing both variants, you will generally find there is
reverse compatibility. However if the sheets are seperate, treat the 'A'
variant a a different chip.

Best Wishes

 

[Chaos Master]

rm -rf /home/Marlowe:

and maybe also a stupid question too ... what is the difference between a
PIC
chip (such as a 16F84) and the "A" version (such as a 16F84A) of that same
chip???

This generally means that the 'A' version has some corrections/new features
when compared to the original version.

[]s

 

[mike]

It varies.
Originally, the 'A' variants were latter, usually faster versions of the
same chips. However some of the more recent 'A' variants, have had as many
differences to the normal version, as other chips using a dfferent
number!. So (for instance), the 16F876A, has the comparator module
present, and differences in it's programming algorithm compared to the
16F876...
In the case of the 84, the original chip was the 16C84, which was flash
programmable, yet used the 'C' designator. Then this had the RAM doubled,
and was sold as the F84. Then the F84A, pushed the clock rate from 10MHz
to 20MHz. In each of these 'steps', the chips were (largely) reverse
compatible, with the F84A, still able to run code written for the C84.
This is not true of the F876A, where the extra initialisation to turn off
the comparator is needed to use F876 code.

Most annoying is the block programmability of the flash. Yes, you need
a different programming algorithm, but you also need a different
algorithm to write the flash and need a different bootloader...and...

Use tools designed for the version you intend to use.
mike

The only answer is to read the individual data sheets. If the latter sheet
is a single sheet listing both variants, you will generally find there is
reverse compatibility. However if the sheets are seperate, treat the 'A'
variant a a different chip.

Best Wishes

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