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'[PIC]: 16F877 or 18F452?'
2002\12\03@040540 by Peter McNulty

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Hi,

I need recommendation on which PIC to choose. I am new to PIC programming, but over the last few days I've been programming a 16F877 until lets say it decided to reach about 100C :)

The 18F452 looks nice and easy to program like the 16F877 however, does it have banks? Looking through the datasheet, is says it does, but then all the PORTx, TRISx, ADRESx and other special functions are all in one table, maybe all in Bank 0? They are roughly the same price it looks like.

Using either chip, I will be converting to the lower model later on for cost/size reasons but would like to test on the 40 pins versions.  I'll be using ADC,  ~10+ outputs, 5V. So which do you recommend?

-Peter

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2002\12\03@043054 by kben

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Hi Peter,
You probably want to start with the newer chip 18F452.
As for banking issues goto piclist.com and look
for the Mailing List Archives, the differences in banking, etc...
were just discussed under the topic tag "[PIC]: 18Fxx2 help"
This thread should answer your questions. I think it started on
November 29th or 30th of this year.


{Quote hidden}

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2002\12\03@050854 by Claudio Tagliola

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Go for the 18, definately. If you can switch, just do it. The 18 is at the
beginning of it's life cycle and all the new exciting things are happening
with the 18's. The 16's are now in the middle, probably only going downhill
from here.

I'm used to working with a compiler, so I don't give a rat's <ahum> a lot
for banking issues, they automagically disappeared when the compiler's done
with it.

Claudio
-----Oorspronkelijk bericht-----
The 18F452 looks nice and easy to program like the 16F877 however, does it
have banks? Looking through the datasheet, is says it does, but then all the
PORTx, TRISx, ADRESx and other special functions are all in one table, maybe
all in Bank 0? They are roughly the same price it looks like.

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2002\12\03@055659 by Andy Kunz

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18F.  If you go with a C compiler (I prefer http://www.htsoft.com) then you can
literally use all the source code from one to the other.  The only things
needing changing are the OPTION and CONFIG registers.

Andy

At 05:06 PM 12/3/02 +0800, you wrote:
{Quote hidden}

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2002\12\03@062230 by Michael Rigby-Jones

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{Quote hidden}

I would recommend starting with the 18F series for a new design.  The
instruction set is better, they have a decent sized stack, loads of RAM, the
banking architecture is much better, some of the peripherals are improved
and you are future proofing yourself.

The 18F data memory does still have banks, but they are now able to access
256 bytes each, and setting the banks is a snap with the special
instruction.  Improvements to the PORT's mean you can set/clear port pins
using the new LATch register without worrying about Read-Modify-Write
issues.  The 18F's have on board programmable brownout reset, and a PLL to
multiply up the clock frequency by 4 times (if you want to).

About the only downside I have found so far is that the ADC S&H capacitors
are more leaky due to the reduction in feature size on the die.  This means
a maximum of 2.5KOhms source impedance is needed for datasheet performance.
The 16F series could use 10K.

Mike

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2002\12\03@064547 by Jan-Erik Soderholm

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Mike wrote :

"The 18F data memory does still have banks, but they are now able to access
256 bytes each, and setting the banks is a snap with the special
instruction."

Note that you can "switch" between one of the all-GPR banks
and the access-bank (with 128 GPR's and all SFR's) just by
setting a flag *IN* the instruction itself. You only have to
add the special bank-switching instruction when selecting
another of the 256 GPR banks.

So you can have access to 256+128 bytes GPR and all 128 SFR's
at the same time without any extra instructions or speed penalty.

And also, the MOVFF can access all 4096 data space addresses
directly. And on the 18F, the WREG is mapped as an SFR, so MOVFF
can move between  W and *any* GPR (or SFR) in *any* bank directly.

*MUCH* better then on the 16F !!

The only thing I miss is a 8-pin 18F :-)

Jan-Erik Svderholm.

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2002\12\03@075522 by Hazelwood Lyle

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After spending a weekend with MPLAB 6.10 and 18F248,
Coming back to work and using the older MPLAB with 16F874
was a bit of a letdown.

Good thing I designed the board to support the 874 OR the
18F458. I told the boss this morning I need a software upgrade
and a few 458's to finish the project.

The RAM banking is much more civilized in the 18F's, but on
the 18Fxx8 (CAN) PIC's there's only 96 bytes of GPR in the
ACCESS register, and not all of the SFR's fit in the remaining 160
bytes. Unless I can keep my total RAM needs at or below
96 bytes, I still need to occasionally play with BSR.

Can anyone offer tips on ISR entry and exit routines with the 18F
chips? There is a bit more built in support, but more choices as well.

Having 2 interrupt vectors, and the option for "fast" register storage
looks real promising,(or confusing). Any suggestions would be
welcomed.

Lyle

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2002\12\03@140156 by Wouter van Ooijen

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> I need recommendation on which PIC to choose. I am new to PIC
> programming, but over the last few days I've been programming
> a 16F877 until lets say it decided to reach about 100C :)

short: in absense of other arguments (available tools, help etc.) just
take the most capable flash PIC, at the moment the 18F452, and
'downsize' later.

long: read http://www.voti.nl/swp

Wouter van Ooijen

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