COMBINED READ-ONLY AND READ/WRITE MEMORY AND METHOD OF ACCESSING THE SAME

摘要

Static memory cells (11) of an array (1) include FET latches for storing read/write data and transfers FETs having a first or a second threshold voltage for storing read-only data. To recover read/write data from an addressed cell (11), a word-line voltage higher than both threshold voltages is applied to word lines (Wo-Wn) by voltage source means (23). To recover read-only data from the same addressed cell (11), a word-line voltage intermediate the threshold voltages is applied under control of a read-only mode line (211) and the resulting voltages on the bit lines (Bo-Bm, B min o-B min m) are decoded (34). Multiple read-only bits in a single cell (11) are allowed by lowering the cell supply voltage when read-only data are addressed.