On Fri, Jun 5, 2009 at 3:46 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
One wonders if
the in-house product test was more rigorous than
connecting two devices with a 2m cable and sending a few characters at
9600 bps...
Or, given that many people seem to have problems with RS232 interfaces
[1], they'd simply claim the cable was wired wrongly, or you haven't set
the baud rate/parity/word length correctly, or... And of coruse support
is non-existant, as it seems to be for all thigns these days :-(
Or tell you just to reinstall the drivers. :-P
Is it possible that the DC-DC converter is playing up?
The USB serial devices I've seen have been a 1-chip design -
presumably USB, UART, and level converters all on one die, with a few
discretes for the DC-DC converter. ?I don't remember seeing any
separate Maxim devices in them.
Ah... I thought I heard of a USB-TTL level async serial chip (i.e. you
need to feed the asynch side through a MAXnnn or similar) and assumed
that's what was used in these adapters. Probably not.
I know there are "FTDI"-based USB seriual converters which would
presumably also have either an external MAXnnn or a bunch of discretes
for a charge-pump and level conversion, but I haven't dismantled any
of those. The ones I have dismantled (by sliding the plastic housing
away from the DE-9) were because they were ultra-cheap (like $4 at the
Thrift Store) to see what it would take to route +5V from the USB
cable over pin 9, since I have a few serial-interfaced devices, like a
toolbooth terminal, that the only external connection is a DE-9 w/pins
2, 3, 5, and 9 passing in/out (TxD, RxD and GND on the expected pins,
plus Vcc on pin 9).
The hack would be simple - sever any connection between the DE-9 pin 9
and the PCB, then run a jumper wire across the inside of the adapter
and reassemble (or in one case, mount inside the enclosure and run the
USB cable out a new hole).
I realize it's no standard, but I've seen power-over-pin-9 enough to
want a simple hack instead of these reverse-Y-cables I've made to tap
serial and either PS/2 or USB for power to run these items. The extra
cable gets a little clunky after a while.
-ethan