> -----Original Message-----
>
> Here's the situation. Those two cables you recommend in that other
> thread are null modem cables. Fine - but I've already learned the
> problem I have is with my usb/serial cable. Soon as I plug it into the
> 102, the 102 screen dims, which may be caused (I've been told) by
> crossed wiring in that cable.
I don't think it's a problem with your particular cable, nor just with crossed
wiring - I have the same screen-dimming issue with both my USB serial adapter
and with a Bluetooth serial adapter, using cables and using low-profile null
modem and gender changer devices. I've always assumed it was load being placed
on the signals the Model T is outputting (DTR, RTS) drawing down one of the
rail voltages, but never really worried about it - I just tweak the contrast
knob a bit and carry on. It's very slight. (I also have had one of my
machines fail a few months ago due to bad capacitors in the -5V power supply
section [no, I haven't got around to ordering the needed caps and replacing
them yet], and I'm a bit suspicious that the -5V supply was weak and was more
susceptible to being dragged down anyway.
> So, even if I do buy another cable (one of the null modem cables), I'd
> still need some kind of usb/serial "converter/adapter". There's no usb
> on the recommended null modem cables, and there's no serial port on the
> Dell laptop or desktop.
There's no getting away from that. Maybe it would be helpful to think of the
USB serial dongle as an interface device rather than an adapter cable, because
that's what it really is. Much in the same way as a USB mouse or USB keyboard
are just ways of connecting a mouse or keyboard to a PC through the USB
interface rather than through the old PS/2 interfaces we used to have, a USB
serial dongle is just a way of adding a serial port to a PC through the USB
interface rather than, say, through an ISA or PCI card the way we used to have
to install them. (or, they'd be built into the motherboard)
Because of what Brian was saying, with regard to the myriad options of serial
cable plug sizes, genders, and wiring schemes, it's not worthwhile for
manufacturers to produce USB serial dongles in all of the possible varieties to
plug directly into each and every possible device out there. Wouldn't it be
great if we could buy a USB serial dongle that had a nice 6ft USB cable and
ended in a male DB25 that was wired DCE? It would plug directly into a Model T
and that would be super, but it's extraordinarily unlikely anybody would make
such a thing because our application is about the only one out there that would
need that particular combination. That's why USB serial dongles are made in a
standard configuration which mimics the real serial ports that were on most PCs
since the 1990s - a male DB9 wired as DTE. It's up to the user to supply the
adapter cable to get from that to whatever connector size/gender/wiring is
needed for the device at the other end.
jim
