Serial port off or locked up?

95LX 100LX

If you are having problems with serial port communications, and your cabling, software and configuration seem to be OK; your serial port is suspect. It may be turned off or locked up. Check to see if it's turned off first:

  1. 1. Try turning the serial port on. ASERCTL <ON DISK ICON> or 100Buddy <ON DISK ICON> let you toggle serial port power on/off on the HP 100LX. HP95CTRL <ON DISK ICON>, TAB95 <ON DISK ICON>, and 95Buddy <ON DISK ICON> let you toggle serial port power on the HP 95LX.
  2. 2. If you're running programs from the DOS prompt on either Palmtop, type serctl /w to turn the port on and serctl /o to turn it off.
If you're still having problems, the port may be locked up. When the serial port does not respond the most common problem seems to be that the UART registers have not been cleared. "UART" is the chip that controls the serial communication in any PC. It has its own memory and registers that store codes or flags that tell the computer its current state. Some programs do not clear the UART registers when they terminate, then when you try to use the serial port it doesn't work. Here are some ways to clear the UART registers:

  1. 1. The easiest way to test the UART flags is to run the self test and test the IR serial port and the Wire serial port. (Close all BUILT-IN applications, turn Palmtop off, and press (ESC)-(ON). Then highlight the desired test and press (ENTER)). The IR port should test ok, and you should get no loop on the Wire port. Just running these test programs resets the UART registers and resolves most problems.
  2. 2. If the problem still persists then do a hard reset (press (<Shift>)-(CTRL)-(ON)). Sometimes doing this several times will clear the registers and get the serial port functioning. This is the equivalent to turning off the power on a desktop PC, which clears the UART registers. (You may need to disable any software that may turn off the serial port. Several programs can be started from the AUTOEXEC.BAT file that can disable the serial port, 95Buddy, 100Buddy, etc.)
  3. 3. If the serial port is still not functioning you can repeat the self test for the Wire serial port with a "loop back" connector in place. This device connects pins 2 and 3 on the 95LX. A loop back connector for the 100LX would connect pins 2 and 3; pins 1, 7 and 8; and pins 4, 9 and 6 connected. (The IR port test is also a loop back test, but it can pick up enough reflection from the Palmtop's case to complete the loop.) It may be advisable at this point to call HP Technical Support (503-757-2004) for help with the loop back test, and to determine if there is a hardware problem.
  4. Rich Hall Editor, The HP Palmtop Paper
  5. Tom Helm HP Technical Support