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Serial port bizzareness
Hello everyone,
I hope some of you guys could help me out? I've got a CNC milling machine hooked up to an old (Pentium 166) PC running Win98 via the 9-pin serial port (com1). It works fine, but no matter what settings I change, I can't get it to work on com2, and more importantly, when I try to get it to run on a brand new PC (which it will have to do, as we want to get rid of the old one) it doen't work properly. On the new PC, it only seems to want to RECEIVE data from the machine, but when I try to TRANSMIT data to the machine, it does nothing. When I tried cables with the Rx and Tx swapped around, it didn't even want to receive data. I've tried it on two other new PC's runing XP with the same results. There are no conflicts and no serial mice/modems etc. Any help you guys can offer would be such a great help! Thanks, -Tone. |
#2
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I am sure you know all this, but I'll go over it just in case:
To a motherboard, there is no difference between Com 1 and Com 2. You can even switch them around in the CMOS settings, assuming your Com ports are built into the motherboard. Now, perhaps something is sharing the com port 2. If you have a device on Com port 4 (like a modem), then it is sharing Com port 2, and that is very bad. Com 1 & 3 devices are shared, Com 2 & 4 devices are shared. You can look in Windows 98 device manager to see what ports show up there. You should see Com 1 and Com 2, and no other Com ports. If you see others, then there is your problem. You can also see that same information when you boot your computer and watch the device listings go by on the blackscreen. If no other com port is there, then you know that probably nothing is sharing the port. That's good. So then one thing you can try is to set Com Port 2 in the CMOS to 3F8 IRQ 4, and set Com Port 1 to 3E8 IRQ 3. Then see what happens. (Normally default setting for com port 1 is 3F8 IRQ 4 and com port 2 is 3E8 IRQ 3.) The other thing is that some motherboards had a wee little ribbon cable to com port 2. If so, it could be defective. You could have corrosion on the Com 2 pins since it is used to little. I wonder what speed the Com port is. Some very old computers had the slower com ports, but I am pretty sure that anything over 40Mhz had the faster ports. Just a stray thought...ignore it. That's all I can think of for now. |
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