Compaq Computer Corporation, Inc.

Christopher D Miller

Ronald B Higgins

Paul M Garner

Glenn A Edgard

A method and circuitry for using two buffers containing video display information is shown. One buffer contains character mask or dot image information, while the other buffer has two portions, foreground and background, which store attribute information. In non-compatible write operations attribute information stored in registers is written to the attribute buffers when mask information is written to the first buffer. In compatible write operations the attribute value is written to the foreground attribute buffer and zero is written to the background buffer, while an OR'ed value of the attribute value is written to the first buffer. In non-compatible read operations the value in the first buffer may be obtained or a CRC value may be generated on the entire character cell. The CRC value can be compared with similar CRC values developed on the character mask of interest to determine if a character is present in the cell. In compatible mode read operations the value in the foreground or background buffer is selected based on the value in the first buffer. In display drive operations a similar selection is made and the value supplied to the circuitry driving the display.

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Houston, TX, United States of America

Christopher D Miller