It may well indeed just be a little excessive drain on the DTR pin by the USB cable, perhaps exacerbated by Vee being a little weak.
I get the same symptom using a USB<>serial cable (CH340) with a straight cable and a mini-null-modem adapter. In fact, I get the same symptom when only DTR (and GND) is connected, as soon as I select TERM. Using the same cable and null-modem plugged into a 'real' serial port only dims the display a tiny bit, which is normal AFAIK. I probably wouldn't worry about it, just disconnect to drop DTR and save some battery time when you're not actively connected. I have some other USB<>RS232 adapters somewhere; when I find them I'll do some more testing. BTW, Kurt: Not that it actually matters, but I think some of those arrows in your chart point the wrong way. m ----- Original Message ----- From: Thomas Morehouse To: [email protected] Sent: Tuesday, April 09, 2019 6:56 PM Subject: Re: [M100] 102 com port power drain? 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]> 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]> 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.
