The DIO-24 provides 24 TTL digital I/O lines. The DIO-24 emulates 8255 mode 0 and has an increased output current of 15 mA (source) and 64 mA (sink) , allowing it to control LED, relay, etc. The DIO-24 consists of three 8 bit bi-directional ports and 2 input lines for interrupt enable and interrupt. The 8 bit ports are named port A(PA),port B(PB) and port C(PC). The port C can be split into two four bit. All ports are configured as inputs upon power-up or reset. The DIO-24 uses 4 consecutive I/O locations in I/O addressing space. The base address is selectable from 200 to 3FF hex. The interrupt signal can be connected to any of the interrupt levels 2 through 7 .