>    I have few working 16F874-based boards.
>    I decided to replace 16F874 by cheaper 16F871
>  as code is about 1K locations.
>  Ordered and received a couple of PIC16F871-I/P
>  $3.6 each from local Microchip folks.
>    Placed them on the boards, programmed with the
>  same code and the same configuration word, verified.
>
>    Now all is working fine, but-t-t start - up time got
>  unacceptable: first 16F871 - 4.4 s, second - 6.3 s.

All these are long shots, but here goes in random mind-blurt order:

1  -  Get rid of the code that disables the comparator since the 871
doesn't have a comparator.

2  -  Make really really sure your code isn't trying to use CCP2 since the
871 doesn't have that either.

3  -  Check for a bug in your code that might have been covered up by the
dead instructions in the extra unused memory space of the 874.

4  -  You should rebuild the code specifically for the 871.  That would
guarantee to catch problems 1 and 2 above.  It would also make sure the
linker didn't decide to stick something into the high addresses of the
874.

5  -  You didn't say what speed crystal you were using, but maybe the
oscillator configuration is marginal and the 874s happened to work but
that batch of 871s aren't as tolerant.

6  -  Look at the oscillator on a scope during these 4 - 6 seconds.  What
is it doing?  Don't forget to switch the probe to high impedence.  Is it
an oscillator problem or a code problem?

7  -  Check what exactly MCLR is doing during the 4 - 6 seconds.

Now that I've looked this list over, start with #4, which allows you to
immediately check off #1 and #2.  Then do #6 and #7 next.  You need to
know what the oscillator and MCLR are doing before chasing after anything
else.

> h2007 - config word (h3FFE)

This means you have low voltage programming and the watchdog timer
enabled.  Both those could be sources of problems.  Add checking out RB3
(LVP pin) to #7 above.

> h2006 - device ID value (h0D21)
> h2005 - (h3F15) - what is it? Does anybody know?

No, this is only for the elves in a hollow tree (cactus) someplace in
Arizona.  Stay out of there.

> h2004 - (0000)
> h2000-h2003 - (h3FFF)


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