General-Purpose 8-Bit I/O Expansion Using an 8742 Microprocessor
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
A technique is described whereby a single-chip microprocessor, e.g., Intel 8742, which is specifically designed for peripheral device controls, is optimized to the extent that the input/output (I/O) pins provide a general-purpose 8-bit I/O path or an 8-bit communication bus in addition to the I/O normally provided. This eliminates the need to add additional microprocessors and control circuitry in applications requiring an 8-bit I/O communications bus in combination with microprocessor functions. Typical use of an 8742 is shown in Fig. 1. However, the technique proposed extends the use of the Intel 8742 to provide an 8-bit communications bus, as shown in Fig. 2, by using three of the Intel 8742 peripheral I/O control pins 11, 12 and 13 and adding external multiplexer 10.