Read/write dual port memory having an on-chip input data register

Abstract

A dual-port memory having an on-chip color register for storage of input data for use in multiple write cycles is disclosed. The color register is written to during a special cycle, which is enabled by a special function pin in conjunction with the write enable and transfer enable function pins, each of which have their logic state latched in during the row address strobe signal. A second type of special cycle causes a multiplexer to select the contents of the color register, rather than the latched data state of the data input terminals, for the data to be written to the selected memory cells. The use of the color register may be used in conjunction with a mask register, where the writing of certain input/outputs is inhibited. In addition, a block write feature may be incorporated with the color register so that, in another type of special cycle, multiple columns per input/output can be simultaneously written with the contents of the color register. The dual port memory containing the color register thus may rapidly store a bit-mapped graphical image where areas of the image are 'filled' with the same color information.