Intel 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. The 8255 provides 24 parallel input/output lines with a variety of programmable operating modes. The 8255 is a member of the MCS-85 family of chips, designed by Intel for use with their 8085 and 8086 microprocessors and their descendants. It was first available in a 40-pin DIP and later a 44-pin PLCC packages. It found wide applicability in digital processing systems and was later cloned by other manufacturers. The 82C55 is a CMOS version for higher speed and lower current consumption. The functionality of the 8255 is now mostly embedded in larger VLSI processing chips as a sub-function. A CMOS version of the 8255 is still being made by Renesas but mostly used to expand the I/O of microcontrollers. The 8255 has a similar function to the Motorola 6820 PIA (Peripheral Interface Adapter) from the Motorola 6800 family, also originally packaged as 40-pin DIL. The 8255 provides 24 I/O pins with four programmable direction bits: one for Port A(7:0) (i.e., all pins in the port), one for Port B(7:0), one for Port C(3:0) and one for Port C(7:4). By contrast, the Motorola and MOS chips provide only 16 I/O pins plus 4 control pins, but the Motorola/MOS chips allow the direction (input or output) of all I/O pins to be individually programmed. Both have configurations that will do a certain amount of automatic handshaking and interrupt generation. Other comparable microprocessor I/O chips are the 2655 Programmable Peripheral Interface from the Signetics 2650 family, the Z80 PIO, the Western Design Center WDC 65C21 (equivalent to the Motorola 6820/6821), and the MOS Technology 6522 VIA and 6526 CIA which had considerable additional functionality such as timers and shift registers. The industrial grade version of Intel ID8255A was available for US$17.55 in quantities of 100 and up. The available Intel 8255A-5 version was for USD$6.55 in quantities of 100 or more.