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The K149 and K150 power the onboard Virtual Comm Port USB-Serial converter chip (FT232BM) from the wall-wart.
When inserting or removing cables from the K149 or K150, the USB driver can get confused unless the cables are handled as follows:
POWERING UP K149/K150:
1. Install the wallwart and powerup the unit first.
2. Install the USB cable.
POWERING DOWN K149/K150:
1. Remove the USB Cable first.
2. Remove the wallwart and powerdown the unit.
The USB hardware at the PC end sees an cable disconnect with a running peripheral as normal, but a disconnect from a non-running (unpowered) peripheral as a fault, and may release the port assignment, i.e. COM5, COM7. The next time the unit comes online, MicroPro may see com port errors until the newly-assigneed com port has been located, especially if another USB peripheral has been installed in the interim. Most people find digging for the new com port as annoying and time-consuming.
A normal, powered release does NOT lose the comm port assignment. That's why K128 and K182 are rarely afflicted with com port changes. If the procedure above is followed, neither will K149/K150 users.