gnupic: DIY USB programmer ?
Subject:
Re: DIY USB programmer ?
From:
David Willmore ####@####.####
Date:
4 Jan 2005 18:14:29 +0000
Message-Id: <200501041813.j04IDmrZ014741@localhost.localdomain>
> I'm looking for a simple DIY design for a USB-based PIC programmer.
> (ok that part is easy)
> ... BUT ... if at all possible such a burner should not require a PIC
> itself. (the chicken and egg problem :( )
Buying a preprogrammed PIC from someone is probably a bit easier than
getting one of the FTDI chips and it's certainly easier than *working*
with them. If you're afraid of getting a PIC programmed SMT soldering
probably isn't your thing, either. :)
> Now, most folks who build PHCC don't have a PIC programmer at home, so
> they need to buy or build one. Of course, the cheaper the better.
> But due to the demise of parallel port and serial port, the common types
> (JDM, Tait, BAJ) can't be used.
> Most new computers only have USB, but no "legacy ports".
>
> I've been wondering if it is possible to build a programmer based on the
> FTDI FT232BM or FT245BM chips.
>
> The problem here is the timing. USB can't guarantee the timings as far
> as I understand.
>
> I've skimmed the programming specs for two chips, and it looked like
> most timings don't have a "max" defined. So, would this be possible ?
Possible or useful?
> What do you guys think ? Could it be possible to build a simple burner
> that does not need "intelligence" apart from an USB interface chip.
I just don't see the benefit.
> I know the FTDI USB chips have a "bit-bang mode".
Yes, and there are some drivers for it, but I've heard of issues with
people who have used it in that it still does not preserve the timing
as they expected it to.
> Your opinions please :)
I'm a bit biased as I'm working on a USB PIC (well, doesn't just have
to be PICs) programmer. It will likely be just one PIC18F2550 or
'2455 with some fairly simple external parts--transistors, resistors,
caps, and diodes. Mostly junk box variety parts. If you squint your
eyes *real hard*, it may look like a Wisp628, but that would be a bit
of an illusion.
To the computer, it will look like an USB->RS232 'dongle', so most
modern OSs will support it with no added drivers--ME through XP,
OSX, and Linux (2.4 and newer) should all work with no extra work
on the OS side. The extra benefit of this is that the host software
is less OS dependent as it just needs to talk to a serial port--which
is a lot easier to 'stub into' an application than talking to some
low level custom USB device.
The protocol that it will speak will look a *lot* like that used
internally in 'PikDev' over the pulseEngine() interface--plus a
little compression. Basically if you say 'do N 1024 times', it
won't send N 1024 times, but send a 'do the next command 1024
times' prefix. The specfic details aren't finalized.
Oh, and don't hold your breath for the final design, the chips just
got released to designers and I expect a *few* bugs in them, so
maybe summer '05?
Cheers,
David
