Your existing usb-serial adapter seems to be perfectly ok as far as we
can tell from anything you've said so far.
It might be a Prolific chip, which is not *ideal*, but it's ok. They
still work well enough for this. We've all used them.
If you want to make it guaranteed, then get the Sabrent cable from that
same wiki page. Same two things I put in a previous email.
But, as far as I can tell, there is no problem with your current
usb-serial adapter.
There might not even be any problem with your serial cable any more either.
Once you got to the point where you can type on one device and see the
characters on the other, you are actually probably good enough, at least
for basic 3-wire software flow control.
The screen dimming is probably going to be the same with any cable and
any adapter, and might be a symptom of weak power supply circuit in the
M100, which might be rectified by replacing some capacitors inside with
new ones.
You could do a little experiment by pulling out some pins on the 25-pin
end of a cable like Kurt did. He only pulled one pin, but you could
actually pull out all the hardware handshaking pins.
Remove RTS, CTS, DSR, DCD, DTR, and RI, (4, 5, 6, 8, 20, 22 ) All you
really need is TX, RX, and SG, (2, 3, 7). Just use needle-nose pliars
and pull those pins right out of the DB25 end of the serial cable. Make
sure you get the pin numbers right! Look carefully with a magnifying
glass and consult rs232 db25 pinout diagrams from google.
Leave all the no-op pins simply for mechanical support to help keep the
plug from falling out of the connector.
(That's a whole other story, how the 25-pin port on the M100/T102 is
actually missing a part, the metal shield, which means plugs plugged in
to it are not mechanically supported the way they are supposed to be,
and so you need all those pins to do the job the shield is not doing.)
This would be a permanent change to this cable. You'd be sacrificing it
to test if disconnecting the flow control lines lessens the screen
dimming, and you'd be making the cable so it's only good for software
flow control from now on.
Then again, maybe a cable that didn't short any of those lines but
actually connected them across to the other end of the cable, maybe that
wouldn't dim the screen either. If you want to test that, get the
Startech cable instead of the Cables2Go cable.
Probably there will be at least a little screen dimming no matter what
cable or usb adapter you use, for reasons Mike explained about how the
circuit for the serial port on the M100 is designed, coupled with the
exacerbating factor that the circuit in the M100 is now also 30-35 years
old, and 30 year old capacitors are going to be weak. They can be
replaced with new ones pretty easily by anyone who works on electronics
at all. "re-capping" is a pretty common task these days that a lot of
people do for a lot of different vintage electronics and game systems
and audio equipment etc. You might be able to find someone local to you
who can do it even if they never saw a Model 100 before. Or I think at
least one person on the list might do it for a few bucks if you ship it
to them. You should replace the internal battery at the same time if you
do look into that.
--
bkw
On 4/10/19 3:29 PM, Thomas Morehouse wrote:
Yep - definitely a neat looking setup!
But if I buy yet another cable - this time one of the null modem
cables recommended on that Tandy wiki page ... don't I still have to
buy a usb/serial converter unit?
As the list members have pointed out, there seems to be a wiring
problem with my current usb/serial unit. So using my current
usb/serial unit is causing the screen voltage problem.
Tom M.
On Wed, Apr 10, 2019 at 3:27 PM Brian K. White <[email protected]
<mailto:[email protected]>> wrote:
On 4/10/19 1:28 PM, Kurt McCullum wrote:
> Perhaps a picture may help.
>
> On the left are the two slim adapters stacked. This ends up being a
> DB9 to DB25 null modem cable. On the right is a USB to serial
adapter.
> The two adapters on the left, get put into the DB9 port on the
right.
>
> The cables that Brian has listed on his site would take the
place of
> the two slim adapters on the left of the picture.
>
> Kurt
That is another nice neat arrangement.
I like it.
--
bkw
