On Sat, Jun 26, 2004 at 11:01:19PM +0200, Jan-Erik Soderholm wrote:
> Byron A Jeff wrote :
>
> > Wouter's basic idea is sound. A single pin interface...
>
> Note the name, " *ZERO*  Pin Loader".
>
> Wouter uses the MCLR pin, not an I/O pin.

Jan-Erik,

I was talking about WLoader, not ZPL. WLoader uses a single I/O pin to do its
job. I do believe that I posted a pointer to the schematic and the WLoader page
in that message, yes?

I've been debating the conceptual merits of the two approaches. Wouter does
a great job of outlining the issues in his ZPL PDF documentation found in the
ZPL ZIP file here: http://www.voti.nl/dwarf/zpl.zip

His transparancy argument for I/O has merit. The short argument is that I/O
is scarce. More scarce than other resources like memory. So it behooves the
bootloader to use as little I/O as possible. Obviously a ZERO pin loader
(actually for nanowatt parts it's a half pin loader as MCLR does share space
with the RA5 input). Would use no I/O. Great, right?!

Well the other side of the debate is twofold:

1) Lack of verification. Since MCLR cannot be an output, the PIC cannot send
any status data about programming back. It's open loop.

2) Loss of debugging interface. See my message to Bob on that discussion.

I'm starting to think that it may be worth giving up one (or an extra half) pin
in order to get these features.

BAJ

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