Multiple programmable initialize words in a programmable read only memory

摘要

A programmable read-only memory (40) is provided which is capable of storing a plurality of initialize words. The memory includes an initialize input lead (9) and appropriate addressing circuitry (7) so that when the appropriate initialize input signal is placed on the initialize input lead, one of several pre-programmed initialize words is placed in the output register (6) of the programmable read-only memory. The word that is placed in the output register is selected according to signals applied to selected address input leads (A.sub.0 through A.sub.3) of the programmable read-only memory. The number of address input signals utilized to determine which initialize word is placed in the output register of the programmable read-only memory is a selected subset of the available address input signals provided to the memory. The described embodiment provides sixteen initialize words using a minimum number of components. The sixteen initialize words are stored in an additional row (12) of the programmable array which contains the memory's normally addressable data words. Because the initialize word circuit (12) is configured as an extra row of the programmable array, the initialize word occupies less chip area than a conventional initialize word circuit. In addition, fewer components are necessary to implement the initialize word circuit of this invention because the inherent selection circuitry of the programmable array is used rather than circuitry which deselects the normal data word provided by the programmable array.