Parallel Port I/O Card with 24-Bit Feature

The 24-bit I/O card project has been designed to function with parallel/printer port of an Amiga or computer using the Intel 82C55 I/O chip.

The design of the device contains read & write strobe, a chip select, and 2 address lines. The Amiga and PC have a limited number of 3 control lines on their parallel ports. At least 8 data pins are lined up even at different pin-outs. The device can be used for reading many input devices.

The interfacing was easily made because the 8255 was designed to operate with 8086 processor and the ISA bus and it will only take some lateral thinking to make it work with parallel port. Only 2.5mA of current per output can be sourced by the 8255 and accessing the device through the parallel port limits the device to around 1 MHz/1 us access time, causing this as one of the limitations. The small current is not enough to drive a standard LED at a reasonable brightness. Fortunately, buffering the I/O devices with a 74245 bus transceiver is usually preferred because it is cheaper to blow one of them up than the 8255.