You don't check continuity on the usb-serial adapter. That isn't just a
cable, it's really a peripheral like a disk drive or a printer, it just
happens to be a peripheral that all fits entirely inside the plug
housing on one end of it. There is no simple direct wire mapping between
the usb pins and the serial pins. Between the usb pins and the serial
pins, there is circuit board with a chip and a few other components
which is converting and translatine between two entirely different kinds
of signals and protocols.
You treat the usb-serial adapter as just a serial *port*, and ignore
that it looks like a wire. Just pretend it's like a serial port built in
to the back of an old desktop.
You check the continuity of the serial cable, which IS "just a cable".
Or, really, you check the continuity of the combined serial cable with
any null-modem and gender-changer adapters, and treat that all together
as one "cable".
--
bkw
On 4/9/19 6:56 PM, Thomas Morehouse wrote:
Thanks Kurt. I'm even denser than usual tonight I guess.
From earlier posts, seems the problem (102 screen dimming) is likely
caused by the usb/serial cable. One end of the cable is a usb plug;
other end is the DB9.
So I'm afraid I don't know how to test continuity on the cable. I can
find pin 4 of the DB9 - but where does the DB25 fit in the picture?
Or, are you saying to test the cable with the DB9/DB25 adapter plugged
into the cable?
Sorry to be the dolt again.
Tom M.
On Tue, Apr 9, 2019 at 10:57 AM Kurt McCullum <[email protected]
<mailto:[email protected]>> wrote:
There are store bought cables that work well. Brian has done a
great job putting together a list of those cables. For my machines
I have a mixture of custom made cables or slim adapters. Both
methods work and give me the pinout below. When you get the cable
right, your M102 will be happy.
But to the question at hand, don't tear apart your cable. Check
it. Right now you know that pins 2,3 and 5 are all going to the
right locations. You will need to check pins 4,6,7 and 8. Since
those are paired lines (4/6, 7/8) one or both pairs will be flipped.
If you have a multi-meter which has a continuity check on it then
you test both ends of the wire.
Here is what I have found to work on all my machines and I include
this in the mComm manual.
7 Wire Cable
PC
Model-T
DCD
1
NC
RX
2
→
2
TX
TX
3
←
3
RX
DTR
4
←
6
DSR
GND
5
↔
7
GND
DSR
6
←
20
DTR
RTS
7
→
5
CTS
CTS
8
←
4
RTS
RI
9
NC
Take one probe of the meter and put it on pin 4 of the DB9 and the
other on pin 6 of the DB25. It should beep or light up (however
you meter functions to indicate a connection). Then do the same
for the DSR line on pin 6 to pin 20. And finally the RTS and CTS
pins 7->5 and 8-> 4. If they are crossed in some manner, then you
will not get a beep or a light.
Hope that makes sense.
Kurt
On Tue, Apr 9, 2019, at 7:38 AM, Thomas Morehouse wrote:
Thanks for the comments gents. Learn something every day.
Kurt, on the "crossed wires" issue, what is the procedure for
fixing the problem? I sure don't want to pull something apart,
or buy even *more* adapters!
Thanks.
Tom M.
On Tue, Apr 9, 2019 at 10:03 AM Kurt McCullum <[email protected]
<mailto:[email protected]>> wrote:
What you are describing happens to me when the either the
CTS/RTS or DTR/DSR wires in your cable are crossed.
Example. The CTS pin listens (checks for voltage) to the RTS
pin on the other end. If you have a cable where RTS goes
straight to RTS and CTS going straight to CTS, then you have
two ends of the cable both feeding voltage to the same wire.
This causes the screen to go dim. the DTR/DSR pins can
produce the same issue.
Kurt
On Tue, Apr 9, 2019, at 5:33 AM, Thomas Morehouse wrote:
Now that I've got my usb/serial link working (M102 to Dell
laptop), I notice the 102's screen get quite dim when the
cable is in the 102's 25 pin serial port.
Doesn't need to be connected to the Dell. Just when you plug
the usb/serial cable into the 102. Unplug the cable, 102
screen returns to normal visibility.
Something to worry about? or just live with it? I wouldn't
have thought the usb/serial cable chip would put such a
drain on the system. Happens with battery power, or even
with external 6 volt poweer.
Thanks.
Tom M.
