BIG 8051 Manual
22
Input / Output ports
The BIG8051 has 10-pin connectors lined to the microcontroller I/O ports. Due to DIP switches SW1-
SW8, every connector pin can be connected to one pull-up/pull-down resistor. It depends on the position
of jumpers J1-J8 to control this aspect.
The pull-up resistor ensures that the signal will be a valid logic level if external devices are connected. A
pull up resistor weakly “pulls” the voltage of the wire it is connected to towards its voltage source level
when the other components on the line are inactive. A pull-down resistor works the same way but is con-
nected to ground. It holds the logic signal near zero volts when no other device is connected.
