Bit Mask Generator
Original Publication Date: 1988-May-01
Included in the Prior Art Database: 2005-Feb-15
A bit mask generator for use in memory accessing comprises a left mask generator, a right mask generator and a bit-wise AND function for combining the two into a full mask. The left mask generator (and similarly the right mask generator) converts a 4-bit input into a 16-bit output. The two 16-bit outputs are ANDed together to produce a full mask having a block of 1s with a block of 0s on each side (e.g., 0000 0011 1111 1000). This is useful in e.g., bit-mapped display systems. The technique used to generate the left and right masks may be extended readily to wider masks, e.g., 64-bit masks. The technique is also useful in monotonic digital-to-analog (D/A) converters. In applications using semiconductor memories (e.g., RAMs) it is often necessary to update selected portions of storage words rather than entire storage words.