Hi,

I'm self-taught in electronics and just diving into the PICs. I would
appreciate any help on the following question, but first here are my
choices, so far :

I'm considering the PIC18F4620-I/P-ND because it has a lot of I/O's (36),
it's fast (40MHz), has flash memory, and 64KB of program memory. Although
it's A/D can sample at only 100 ksps. Therefore I would disable the internal
A/D and ad my own external A/D, preferably over 1msps.

If I had to settle for 200 ksps A/D sample rate :-((( then I would pick
PIC18F4431-I/P-ND, which samples at 200 ksps, 40MHz, flash memory, 36 I/O's,
and 16KB of program memory.

This is a budget project so I would like to build my own programmer. Here's
one site that seems interesting, which includes the above PIC chips:
http://hyvatti.iki.fi/~jaakko/pic/picprog.html


1) I've searched for typical power consumption for most PIC18F chips and
have only seen Power Dissipation under Absolute Maximum Ratings, which seems
to always be 1W. Is that typical power consumption? I'll be using the chip
at full speed 40MHz. If I use an external A/D then perhaps there's a way of
disabling the internal A/D and saving some power.

2) I'd like to achieve A/D sample rates up to 1 msps. This seems possible
only with DSC's. Therefore, I'd like to ad an external A/D. I gather that
the PIC18F ports are also TTL compatible. So the A/D output bits can hook
directly to do MCU ports. Does anyone know how many cycles it takes to read
one of the 8 bit ports in TTL mode (not analog)?

3) I referred to a url link above that freely provides a programmer circuit
which seems to work with PIC18F4620 and PIC18F4431. Does anyone have any
experience or knowledge about that programmer? Any possible foreseen
gotchas? From what I can tell in the datasheets, it seems that if a
programmer works for a particular PIC18F chip then it will work on any
PIC18F chip. If this is correct then perhaps I should build a more popular
PIC18F programmer.

4) Is it unreasonable to try and program this in asm verses C? Eventually
I'd like to buy Microchip C18 toolsuite, but not right now. Has anyone tried
the free cpik on any PIC18xxx chips? They list numerous PIC18F chips that
cpik should work on, but I don't see PIC18F4620 or PIC18F4431 listed. Here's
there website :
http://pikdev.free.fr/
http://pikdev.free.fr/download-cpik.php3

5) The programmer I'm looking to build is serial port. I'm trying to get an
idea how long it will take to program 64KB. I calculate at 9600 baud it
would take over 50 seconds. Does that sound about right length of time?

I appreciate any advice or help,
Paul
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