> but technically the 18F4550 and family
> DO have a maximum time parameter: P17, MCLR fall to VDD fall, max 100ns.
> See DS39622.
interesting given that at least one of microchips own programmers (the ICD2) can't follow that (since it doesn't control VDD) and yet programs the chip fine i'd take it with a pinch of salt.

maybe that figure is for if you have MCLR disabled, an oscilator availible during programming (either intosc or programming in cuircuit) and you don't wan't the pic to start running in the programming setup. 

> 
> Actually, I wanted to add one other (potentially more serious, but also
> maybe weirder) comment: our primary complaint is that we only have USB
> ports to work with. Well, ignoring the other complaint about
> platform-specific software, how about this: doesn't the USB
> specification require that a particular USB port can have its power
> switched on or off under software control? Why not use the USB +5V
> supply line as a twiddle pin? It would need a kernel-mode driver, sure,
>  but it could work (unless I'm quite mistaken about that part of the
> specification - I thought you had to enable power to only one port at a
> time in order to give a device an address before bringing another
> unconfigured device onto the bus).
don't think so, despite the name USB IS NOT A BUS it is a tree of point to point links and the ports always seem to stay powered (except when you short them out ;) ).

and even if it does turn out that usb ports are supposed to be able to have thier power switched from software i'd be willing to bet that it would be even more of a compatibility nightmare than handshake lines on serial ports.

now for some more comments related to this thread (in no particular order).

One thing i've wondered for a while, is it possible to program a bootloader using LVP and then use self programming to disable LVP? the specs say you can't use LVP to disable LVP but they say nothing about if you can use self programming to do it. Has anyone tried this?

also for building an intelligent programmer losing an IO pin is hardly critical 

afaict USB-whatever (serial parallell GPIO etc) converters will always have the problem for bit banging that USB is fairly high latency, the only real way arround this is to have something programmable at the device end of the usb link (e.g. a pic18f2550) and code the bit banging there

one thing i think would be helpfull is a site selling pics programmed to order so those of us who design pic based projects but don't want to get into online sales ourselved could just upload our hexfiles to it and put up "buy your pre-programmed pic here" link. Its not nice for a newbie to find that they have to build a crappy serial programmer or buy a fairly pricy programmer before they can start on building a decent programmer (or building some other pic based project they found on the net).

I dissagree about the idea that someone starting with pics and going down the build your own road is unlikely to have some collection of parts already. I'd think that someone with no electronics knowlage would be far more likely to buy a ready designed demo board. I'm sure there are plenty of people with a fair level of electronics experiance but who have never used pics before.

BTW to the piclist.com webadmin, it seems that just reading through a long thread page by page in a normal web browser triggers your bot detection code every few posts.


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