Standalone low-cost interface, controller and emulator for the apple II

Personal computers which have I/O slots for the insertion of plug-in interface cards are widely used in laboratory and other applications where realtime control and data acquisition are required. Two of the most popular personal computers used in this way are the Apple II and the I BM Personal Computer. The Apple II has an eightslot I/O bus and 2k addresses reserved in the memory map for I/O use, while the IBM PC has a five-slot I/O bus, and a separate I/O address space for this bus. In this paper we describe an I/O interface card for the Apple II. The card is designed to be plugged into one of the Apple II's slots. The card provides the Apple II with two parallel ports, two programmable timers, a simple serial interface and a 2k EPROM. The unique feature of the card is its ability to act as a standalone microcomputer independently of the Apple II, once the card has been interfaced to external equipment or devices. It can then be used as a controller or in any other application where a microcomputer of modest capability is required. The design principles adopted can be applied to any other microcomputer system with an I/O bus, such as the IBM PC.