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'[PIC:] Migration from 16F628 to 18F452'
2003\11\27@084350 by Rafael Vidal Aroca

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   Hi, i'm migrating a 16F628 based system to 18F452 and would like
just to confim some things i've searched:

   1. 18F452 can be programmed with picstart plus, right?

   2. May I use the code I have running in 16F628 in 18F452 with no
changes, or at least few changes?

   3. The 1,5K of memory that 18F has is all available for user?

[]s Rafael.

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2003\11\27@085223 by

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Rafael Vidal Aroca wrote:

> Hi, i'm migrating a 16F628 based system to 18F452 and would like
> just to confim some things i've searched:
>
> 2. May I use the code I have running in 16F628 in 18F452 with no
> changes, or at least few changes?

Maybe you *should* change whatever you can to make full use
of the better 18-series instruction set. You'll get code that
is easier to read and modify and possibly also running faster.

> 3. The 1,5K of memory that 18F has is all available for user?

You have 1536 bytes of RAM to use. Who else would use it ?

Jan-Erik.

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2003\11\27@090257 by Wouter van Ooijen

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>     1. 18F452 can be programmed with picstart plus, right?

IIRC it can, with the right firmware. Check the 'supported targets' list
for the firmware

>     2. May I use the code I have running in 16F628 in 18F452 with no
> changes, or at least few changes?

Only if you have used a development system that is designed to hide such
a target change from you, in that case you might get away with a
re-compilation. But the 14-bit (16F) and 16-bit (18F) PICs are quite
different (much more than 12 and 14 bit cores), down to the same
instructions (when they exist) having slightly different effects.

>     3. The 1,5K of memory that 18F has is all available for user?

yes, and in a much more transparent way than on 16F's

Wouter van Ooijen

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2003\11\27@091129 by Olin Lathrop

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Rafael Vidal Aroca wrote:
>     Hi, i'm migrating a 16F628 based system to 18F452

That's quite a jump.  18 pins to 40, 2K to 16K words program memory, 14 to
16 bit core.  That's practially a new design, not a "migration".

>     2. May I use the code I have running in 16F628 in 18F452 with no
> changes,

Of course not.  The two processors have different instruction word sizes for
one thing.  If you wrote the original code with portability in mind, or used
something like my development environment (http://www.embedinc.com/pic) then
the source code only requires minimal changes and a rebuild.  If you didn't,
it's going to be more tedius.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2003\11\27@093832 by Harold Hallikainen
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A more common "migration" would be from the 16F74 or 16C74 to the 18F452
or 18C252. Microchip has an ap note on this migration. The 18 has several
more instructions that can simplify your code, but you don't have to use
them right away. The 16 and 18 behave a little differently on setting
flags or condition codes, especially on increments and decrements. Watch
for that. Also, the word size changes the way you do jump tables. You have
to shift left, then do a branch instruction. The goto is a 4 byte
instruction, so you'd have to do two shifts to use it. Also, bank
switching is considerably easier. There are more FSRs, and they are bigger
(high and low byte).

I'd have a look at the above mentioned ap note, change to the appropriate
Microchip include file, and test your code!

Harold


> Rafael Vidal Aroca wrote:
>>     Hi, i'm migrating a 16F628 based system to 18F452
>
> That's quite a jump.  18 pins to 40, 2K to 16K words program memory, 14
to 16 bit core.  That's practially a new design, not a "migration".
>
>>     2. May I use the code I have running in 16F628 in 18F452 with no
>> changes,
>
> Of course not.  The two processors have different instruction word sizes
for
> one thing.  If you wrote the original code with portability in mind, or
used
> something like my development environment (http://www.embedinc.com/pic)
then
> the source code only requires minimal changes and a rebuild.  If you
didn't,
> it's going to be more tedius.
>
>
> ***************************************************************** Embed
Inc, embedded system specialists in Littleton Massachusetts (978)
742-9014, http://www.embedinc.com
>
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