8255

The Intel 8255 (or i8255) programmable peripheral interface (PPI) chip was developed and manufactured by Intel in the first half of the 1970s for the Intel 8080 microprocessor and is a member of the MCS-85 Family of chips. The i8255 was also used with the Intel 8085 and Intel 8086 and their descendants and found wide applicability in digital processing systems. It was later cloned by other manufacturers. It is available in 40-pin DIP and 44-pin PLCC packages. The 82C55 is a higher-speed CMOS version.

The i8255 provides 24 parallel input/output lines, but the functionality of the i8255 is now mostly embedded in larger VLSI processing chips as a sub-function. The i8255 is still made and is often used to expand micro controller input/output.

The i8255 has a similar function to the MOS Technology 6522 (Versatile Interface Adapter) and the MOS Technology CIA (Complex Interface Adapter) all developed for the 6502 family. All of these chips were originally available in a 40-pin DIL package but the i8255 provides 24 usable I/O pins whereas the MOS chips only provide 16 I/O pins plus 4 control pins. However, the MOS chips contains other functions besides pin I/O, such as two programmable reload timers and a simple I/O shift register function. Furthermore, the MOS devices allow the direction (input or output) of all their I/O pins to be individually programmed. The i8255 I/O pins have only four programmable direction bits: one for all of Port A(7:0), one for Port B(7:0), one for Port C(3:0) and one for Port C(7:4).

Other comparable I/O chips are the 2655 Programmable Peripheral Interface from the Signetics 2650 family, the Motorola 6820 PIA (Peripheral Interface Adapter) from the Motorola 6800 family and the Western Design Center WDC 65C21.

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