The CIO-DIO24 low-cost digital I/O board is designed for use with IBM PC/XT/AT or compatible computers. The board employs one 8255 digital I/O chip, controlling 24 digital I/O lines, and consists of three ports: an 8-bit PA port, an 8-bit PB port, and an 8-bit PC port. The PC port may also be used as two half ports of 4 bits. Each of the ports and half ports may be configured as input or output by software control. After RESET (power up of computer), all ports are set as inputs.