Microcomputer system employing program cartridges

Claim 1

A microcomputer system comprising, in combination, a microcomputer and a program cartridge removably mounted into the microcomputer, said microcomputer comprising internal read-only memory means having an address input, a select input and an enable input, address means for driving an address bus coupled to said address input, select means for selectively driving a plurality of select lines, including a first select line coupled to said select input, enable means for energizing an enable line coupled to said enable input, and socket means connected to said address bus, said select lines and said enable line, said program cartridge including plug means for mounting into said socket means, external read-only memory means having an address input and a select input, an external address bus for connecting the address input of the external memory means to the address bus of the microcomputer through the plug and socket means, a plurality of external select lines, each including a selectively connectable link, for selectively connecting the select input of the external memory means to said select lines, including said first select line, in the microcomputer through the plug and socket means, and a disable line including a selectively connectable link, for selectively coupling disabling means in the cartridge to said enable line through the plug and socket means, whereby, upon insertion of the plug into the socket, the external memory means supplements or replaces the internal memory means in accordance with selective connection of said links.