> A serial port normal does supply power, so it does produce a drain. 'Real' serial ports not usually but yes, definitely many USB serial 'ports', BT dongles, etc. do.
A 'real' RS232 port as found on older PCs etc. is usually powered by separate + and - 12V supplies and doesn't draw any current from the port aside from the input impedance of the receivers. But since the USB side of a USB<>serial cable only supplies 5V but the RS232 side needs anywhere from +/- 3 to 15V, the RS232 power is often derived from one or more RS232 pins, especially DTR, on the assumption that there's power to spare (normally +/- 12V). But the Model T serial ports are fairly weak +/- 5V through resistors, with the negative side sourced from the same supply as the LCD, so it's not surprising that the display is sensitive to any current drawn on the RS232 pins. m ----- Original Message ----- From: Tom Dison To: [email protected] Sent: Wednesday, April 10, 2019 1:15 PM Subject: Re: [M100] 102 com port power drain? A serial port normal does supply power, so it does produce a drain. On Wed, Apr 10, 2019, 12:09 PM Stephen Adolph <[email protected]> wrote: fwiw, I usually see the LCD change it's bias when I plug in serial. On Wed, Apr 10, 2019 at 1:03 PM Kurt McCullum <[email protected]> wrote: Is your current USB to serial adapter an entire cable? For example, one side is a USB plug and the other is a DB25 male plug? With no other parts in between the two? Kurt On Wed, Apr 10, 2019, at 9:54 AM, Thomas Morehouse wrote: Thanks Kurt. But we already know that my current usb/serial adapter (which is a single unit usb/serial cable) cause the 102 screen to dim. In other words, that's where the problem is. So I don't see how a new null modem cable plugged into my faulty usb/serial adapter/cable will help the situation. Tom m. On Wed, Apr 10, 2019 at 12:51 PM Kurt McCullum <[email protected]> wrote: Tom, The cables that Brian is recommending will attach to your existing usb to serial adapter. So the connection would work as follows. Laptop USB Port -> USB to Serial Adapter -> DB9 to Db25 Null modem Cable -> Model T Kurt On Wed, Apr 10, 2019, at 9:46 AM, Thomas Morehouse wrote: Thanks Brian. Turns out your cable links weren't in my thread at all. They were in a different thread completely which I wasn't part of, and wasn't following. 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. 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. Thanks. Tom M. On Wed, Apr 10, 2019 at 12:39 PM Brian White <[email protected]> wrote: In one post, I provided a link directly to two items, a specific cables2go cable and a specific sabrent usb-serial adapter, so that you wouldn't have to make sense of the full page where that info came from. And also linked that full page, which includes the startech and others. http://tandy.wiki/Model_100_102_200_600_Serial_Cable I know reading that full page might not make 100% sense, because it's a lot of verbiage, and there are many cables listed there and they all work for this so how do you choose, and some parts are kind of cryptic, which is why I pulled out the two parts to get. For instance the shorthand I used to document each cables wiring idiosyncracies, like "DCD<>DSR+DTR", I know that part is cryptic. When I was testing cables and assembling the info, I just needed to get the key details written down, and the form didn't matter. I could expand it to be more readable later. What those little things are showing is how each particular cable differs from the rs232 spec. For instance "DCD<>DSR+DTR" means that dsr and dtr are tied together on one end, and connected to dcd on the other end, and that it's the same on both ends in both directions. All other connections are according to the rs232 spec, and you get the pin numbers and positions from the rs232 spec. Some time when I want to spend more time on that page, I can expand those to a less cryptic form, (or anyone else can, it' s a wiki) but until then at least the knowledge is documented so that later I can refer to it. It's sort of like working notes until then. Mike Stein also provided a direct link to a specific monoprice cable. That one is good too. (it's on that page too for instance) All other cables you randomly find from wherever, probably aren't right without some kind of adapters, and there is no way to tell if the wiring is right except by knowing the rs232 spec and testing the connections. rs232 is not a single thing, it's a spec with a bunch of options and configurations. In order to use anything serial, you the user, actually has to understand that spec, or, you have to take the word of someone else who does, and says "this specific cable will work for this specific application". Plugging in any old cable without knowing how it's wired or what the different rs232 signals are for and how they work, will never work. Serial is not like usb or ethernet or headphones. For another example of ehat I mean, even when you finally get a correct serial cable for connecting your m100 to a pc, that cable won't be correct for connecting to a modem, or a plotter, etc. 3 different devices, 3 different cables, and yet all of them are valid correct serial cables even though they are all different from each other. The only way to make it work is to understand that and go read about serial cables so that you know enough that you could build your own from scratch, or continuity test any off the shelf cable to fully understand what it does. Or, buy one that is already known to be correct for this particular task. -- bkw On Wed, Apr 10, 2019, 7:30 AM Thomas Morehouse <[email protected]> wrote: Brian - you wrote: " The Cables2Go one I linked is all the same, except it also has rts/cts, so it works with HTERM, as well as everything else. And finally, the StarTech one I linked, is also all the same, but without shorting DCD to DSR, or shorting DTR to DSR, which means that one should cause the least possible drain on any possibly weak power rails in the M100. All this mystery has already been completely figured out and nailed down. One mouse click and $7 later and you're done." I've gone through all your posts in this thread, and find no links for Cables2go or StarTech. I'm absolutely going nuts here, trying to figure out how to do things, and how to follow advice. One post with advice raises a question, someone else tries to answer the question, then someone else tries to clarify the answer to someone else's question. Really helpful to some, but frustrating to me. Which post had those two links for the proper cables? I've now got two usb/serial cables which don't seem to work, plus several male/male, female/female, and DB9 to DB25 adapters. Total so far: $100. As I can't find the links Brian referred to, I don't want to guess and buy yet another thing which might not work. Thanks. Tom M. On Tue, Apr 9, 2019 at 9:34 PM Kurt McCullum <[email protected]> wrote: Tom, Looks like you will need to either build or buy a cable. My two cents is below but I'm sure others will chime in. There are several options out there. Here is a description of what I do with all my Model-T units. I start with this DB25 to DB9 adapter which is just a regular DB9 to DB25 converter. I attach these with some 2.5mm (should be 2.6mm) screws to the Model-T so its always attached. https://www.sfcable.com/db9-female-to-db25-male-serial-mini-adapter.html Then I put one of these adapters in between the DB9 serial port and the 9-25 adapter which creates a null modem cable. https://www.sfcable.com/null-modem-adapter-db9-db25/db9-male-to-female-null-modem-mini-adapter.html For my T200 I have remove pin 1 from the null modem adapter to make it happy but that's a quick fix with needle nose pliers. Everybody has there preference on cable setup so eventually you will come up with a solution that works for you. Sounds like what you have is working for text transfers so that's a start. Kurt On Tue, Apr 9, 2019, at 5:59 PM, Thomas Morehouse wrote: Thanks Kurt. Testing the DB9-DB25 adapter only - not the usb/serial cable - I have continuity NOT from pin 4 of the DB9 to pin 6 of the DB25. I have continuity from pin 4 of the DB9 to pin 20 of the DB25. That's using the numbers printed at the pins themselves. Should I even bother testing the others you suggest? Sounds like the adapter already fails the test. Tom M. On Tue, Apr 9, 2019 at 8:48 PM Kurt McCullum <[email protected]> wrote: Ignore the USB to serial piece of the puzzle. As Brian said, it's just a serial port. Test the 9 to 25 adapter. One end will be female so it's easier to put something like the end of a paper clip into one hole at a time then put the probe on that. Kurt On Tue, Apr 9, 2019, at 5:22 PM, Thomas Morehouse wrote: OK - looks like I wasn't clear. In Kurt's post, he writes: "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." If the usb/serial cable is a single unit (usb at one end, DB9 at the other), how do I put one probe of the meter on the DB9 and the other probe of the meter on the DB25? There's no DB25 on the cable, unless I plug the 9-25 adapter into the DB9 - but then I can't put a probe on the DB9. Jeez I feel dense. I'm really sorry I can't follow this, but maybe I'm just overlooking something really simple? Thanks. Tom M. On Tue, Apr 9, 2019 at 7:56 PM Brian K. White <[email protected]> wrote: 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. >>> >> >
