SLAU278AH May 2009 – March 2021
Some PCs do not supply 5 V through the parallel port
Device identification problems with modern PCs, because the parallel port often does not deliver 5 V as was common with earlier hardware.
Measure the voltage level of the parallel port. If it is too low, provide external 5 V to the VCC pads of the interface. The jumper on a the target socket must be switched to external power.