Microcomputer with programmable multi-function port

TL;DR: A single-chip microcomputer comprises a CPU (1), a RAM (2), a ROM (3), a timer (4), serial I/O communication logic (5, 6, 7, 8, 9, 10, 11, 12, and 14) and various power supply, clock, and control inputs as discussed by the authors.

Abstract: A single-chip microcomputer comprises a CPU (1), a RAM (2), a ROM (3), a timer (4), serial I/O communication logic (5), four I/O ports (11-14) and various power supply, clock, and control inputs One of the I/O ports (13) is user programmable by application of specific signals to mode selection pins (P20-22) for configuration in several possible ways The programmable port comprises a plurality of lines which each may be individually programmed as input or output lines to peripheral equipment associated with the microcomputer Alternatively, the port lines can be programmed to serve as a bidirectional data bus to external memory Alternatively, the port lines can be programmed to be multiplexed data and address lines to external memory Bus arbitration logic is provided to route data to the CPU from either on-chip memory or external memory