MULTIPLEXED SERIAL REGISTER ARCHITECTURE FOR VRAM

A dual-port DRAM in which a single serial latch is shared between two pairs of folded bit lines from two arrays of memory cells (10, 20). A first set of multiplexer devices (14, 24) selects one of the two pairs of folded bit lines from each of the arrays (10, 20), and a second set of multiplexer devices (16, 26) selectively couple one of the remaining folded bit line pairs to either the parallel port or the serial latch for access to the serial port. This arrangement greatly decreases the consumption of chip real estate. At the same time, it makes unlimited vertical scrolling possible through the use of a copy mode that can be carried out in two operating cycles, and facilitates masked writing, while at the same time reducing clocking complexity.