INS8255N

~National ~ Semiconductor APRIL 1978 INS8255 Programmable Peripheral Interface General Description The INS8255 is a programmable peripheral interface contained in a standard, 4().pin dual·in·line package. The chip, which is fabricated using N·charinel silicon gate technology, functions as a general·purpose parallel input/output interface in National Semiconductor's N8080 microcomputer family. The functional configura· tion of the INS8255 is programmed by the system software so that normally no external logic is required to interface peripheral devices. The INS8255 has three basic modes of operation that can be selected by the system software. In the first mode (Mode 0), the INS8255 provides simple input and outqut operations for three 8·bit ports. Data is simply written to or read from a specified port (port A, 8 or C) without the use of "handshaking" signals. In the second mode (Mode 1), the INS8255 enables the transfer of input/output data to or from a specified 8·bit port (Port A or BI. in conjunction with strobes or "hand· shaking" signals. Ports A and B use the lines of Port C in this mode to generate or accept the "handshaking" signals with the peripheral device. In the third mode (Mode 2), the INS8255 enables communications with a peripheral device or structure via one bidirectional 8·bit bus port (Port A). "Handshaking" signals are provided over the lines of Port C in this mode to maintain proper bus flow discipline. Features Outputs Source 1 mA at 1.5 Volts 2...