Abstract: A video controller integrated circuit is provided with an on-chip test data generator within the integrated circuit for emulating an external memory for testing purposes. When activated, the test data generator generates a pseudo-random data stream which is fed to the data input of a video memory controller within the integrated circuit. A signature generator, also within the integrated circuit generates a characteristic signature from the data stream which is compared to a characteristic signature from a known good integrated circuit.

Abstract: An apparatus for selecting a reference line for image data compression including a plurality of mutually connected reference selector chips for selecting a reference scan line from vertical mode coding of image data. The reference selector chips select a reference scan line from a plurality of preceding scan lines in exclusive or combination of the image data of each candidate reference scan line with the image data from the input scan line. The candidate reference scan line that has the lowest number of dissimilar bits is selected as the reference scan line. Each candidate reference scan line has associated therewith a register having bit positions arranged from the highest order bit position to a lowest order bit position for storing a binary sum of the number of dissimilar bits. When the sums are compared, the binary value and successive bit positions are compared from the highest order bit position to the lowest order bit position.