Re: inputs to 89C2051???
Pull-up resistors are used because the pin drivers are open-drain. That means that they can connect to 0V, but not to +5. Without the pull-ups, when set to output 1, the output will just float. With the pull-up, the pin is connected through the resistor to +5V when output is set to 1.
This is why an LED, for example, is usually connected between the pin and +5V, rather than ground.
To use as inputs, just define them as input (write '1' to them), driving the pin high through the pull-up. You can then give the pin 0 or +5V and read its value. When giving it 0, the pin will source current through the pull-up resistor. Your driving circuit must have a lower impedance than the pull-up resistor, or it might not pull down to 0 enough (it makes a potential divider with the pull-up). Note also that no connection to a pin will read as a '1' due to the pull-up.
FoxyRick.