Two-Step Mix for Graphics Display Update
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
In updating an all-points-addressable graphics display, new binary data is mixed with old picture data according to a four-bit truth table. Two-step time-multiplexed logic is disclosed to perform this mix which is particularly useful when a large number of pels (picture elements) are updated in parallel. When updating a graphics color display, it is required to bitwise combine two n-bit input values according to a four-bit programmable truth table. There will be an n-bit result which is to be latched. The same truth table is to apply for all bits. Fig. 1 shows prior-art logic to perform this bitwise mix. A(n) and B(n) select the appropriate bit from the truth table, which is then latched in the result (n) register. Repeat logic inside dotted lines is provided one for each bit (64 copies for 64 bits).