19 Jun
2013
19 Jun
'13
12:25 p.m.
On Jun 18, 2013, at 14:48, ard at p850ug1.demon.co.uk (Tony Duell) wrote:
THat comment was somewhat tongue-in-cheek based on Chucks comments on how
simple it is to make a USB slave device...
Thers's a nice little project for somebody
(given that USB is claimed to
be simple). Make a device with a USB port on one side (and which behaves
like a normal USB-RS23s converter) and which will do the slower baud
rates (it needn't go above 9600), including 110 and 45.45 baud.
USB is simple in a very limited sense, in that there are only two signal wires and bit rate is auto-negotiated. Obviously, the
auto-negotiation
itself is complex, but it's taken care of for you (so, again, a very limited
definition of "simple"). For example, what you've proposed is pretty
Most things become simple if somebody else does most of the work....
hard to do, starting with the fact that there are no
"normal" serial
converters for USB; there are standard classes for things like mass
storage, audio converters and human interface devices, but absolutely
none for serial converters. So it's all custom, which means you either
And I suppose there isn't a standard class for a simple chracter I/O
device....
have to make something which apes one of the popular
existing chips
out there (which is both a monumental task and also probably doesn't
solve the problem because it's often in the drivers) or write your own
drivers to go along with your custom USB solution (which means you
have to support at least three OSes if you want to keep people from
whining, and you have to figure out how all those different Linux distros
want third-party drivers to be installed).
Exactly... That's one reason why I have come to hate USB (there are
plenty of others).
OK, make said device appaear as an FTDI converter IC (since drivers for
that are pretty much standard) but with the required baud rates. Heck,
make it ignore whatever commands are used to set the baud rate but to
ahve eitehr an physical switch to select the baud trate or a pin to feed
in a 16* clock .
-tony