On the 8255 the Port B pins are set to all inputs or all outputs. If Mr. Wo is using one port B pin for as input to see a switch or some such then all the other port B pins are also inputs as well.

The part is supposed to have a "bus hold" circuit on each pin to set the held state of the pin without pullups or pull down resistors. For myself I like to tie the unused pins to Vcc through a high valued resistor like 47K.

When Frances reads the port B into software all he really needs to do is to AND the byte read from the port with the value &H01. This will isolate the bit from Port B bit 0 and clear all the other bits from the other input pins that are to be either pulled up or pulled down.

Michael Karas