Method of employing in turn add-on read-only memory devices in a data processor with verification of their availability and validity

摘要

A data processing system includes a processor (10), base read-only store (101) and a non-volatile read/write memory (104) interconnected by a control bus (13), a data bus (19), an address bus (14) and a selection bus (18). Add-on read-only memories (106, 107) can be coupled to the busses when required to add operating features to the system. The read/write memory (104) includes a table containing a location for each possible add-on memory. Each location contains data indicating either that the related add-on memory is connected and required by the system, or is not connected, or, if connected, not required. Each add-on memory stores, in its first location, the address of that location for verification when it is accessed.