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peter green wrote:
[snip]
> 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 ;) ).

I'm not sure about that. I was under the impression that a hub, when
brought online, was required to power up one port at a time, since the
newly-powered device gets the unconfigured address and must be
configured before another device can be brought up. Again: I'm not sure.
I have the USB specifications, but I haven't read them yet. This is just
my impression.

> 
> 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.

But since the ports are real hardware, they must act (at least at the
hardware level) properly. I can see using some kind of Linux LiveCD with
the sole purpose of booting a custom kernel with the weird USB driver
and burning a pre-written hex file to a chip.

> 
> 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?

It sounds insanely dangerous. I can't see anywhere in the datasheet
which says it's impossible, but you have to erase a full block at a
time, and erasing the configuration registers blows away your USB
voltage regular, oscillator configuration, WDT, BOR, and all sorts of
other quite important things. If you're only trying to WRITE (i.e. only
change a 1 to a 0), it might be more doable in theory.

[snip]

> 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.

I fully agree with this. A little while ago, that was my exact
situation: I had done some electronics, but never seen a PIC before. I
wanted to get into PICs, but I didn't really see any way to get in other
than building my own programmer. I don't think my local electronics
shops even carry programmers. Today, I'd have no problem ordering a
programmer from Wouter or Olin, but back when I was first getting into
PICs, their names didn't mean anything to me - so I wasn't exactly going
to send them money. The point is, a soldering iron is something I can go
to a shop and look at before buying - I'm guaranteed to receive what I
pay for. I can't get a programmer at a local shop.

[snip]


Chris
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