Serial Port Trouble

john7 · 06-09-2005, 10:35 AM

I remember at some point I heard there was a way to check serial ports, both 9pin and 25pin by touching two pins together with say a screw driver. If the port was working it would echo (in notes) any letter key pressed on the keyboard while these particular pins are "jumped". Thank You for having this website. john

**UncleMacro** · 06-09-2005, 05:54 PM

Well, if you're only connecting two pins then it would have to be transmit data to receive data which would be pins 2 and 3. Check here for the gory details on loopbacks. You'll need a program which is both transmitting to the serial port and reading from it to do any checking. Just connecting transmit and receive together isn't going to do anything on its own. Some programs will work with just the two pins shorted but most won't. There are two other handshake signals which programs can check for. Just shorting the transmit and data pins won't do the handshakes.You'd need the full loopback plug as shown on the webpage to make those programs work properly.

06-09-2005, 10:35 AM	#1 (permalink)
john7 Registered User Join Date: Jan 2005 Posts: 4 OS: Win2000	Serial Port Trouble I remember at some point I heard there was a way to check serial ports, both 9pin and 25pin by touching two pins together with say a screw driver. If the port was working it would echo (in notes) any letter key pressed on the keyboard while these particular pins are "jumped". Thank You for having this website. john

06-09-2005, 05:54 PM	#2 (permalink)
UncleMacro TSF Enthusiast Join Date: Jan 2005 Location: San Diego Posts: 2,133 OS: Vista SP1 My System	Well, if you're only connecting two pins then it would have to be transmit data to receive data which would be pins 2 and 3. Check here for the gory details on loopbacks. You'll need a program which is both transmitting to the serial port and reading from it to do any checking. Just connecting transmit and receive together isn't going to do anything on its own. Some programs will work with just the two pins shorted but most won't. There are two other handshake signals which programs can check for. Just shorting the transmit and data pins won't do the handshakes.You'd need the full loopback plug as shown on the webpage to make those programs work properly.