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Line compare           index 18h  CRTC

Layout  b7-b0  LC   Line compare

        This register allows split-screen display.

        When the line counter is equal to the 10-bit line-compare
        value, the refresh address will be cleared, causing the
        horizontal display lines beneath the line compare value to be
        refreshed from display memory address 0. The effect is a
        dual-screen operation. This register contains the low-order
        eight bits of the line-compare value; bit 8 and 9 are found in
        the Overflow and Max scan line registers.


        Refreshed from  > +-----------------------------+ Row 0
        address in        |                             |
        Start Address     |          Screen 0           |
        registers         |                             |
                          |                             |
        Refreshed from  > |-----------------------------| Row = Line
        address 0         |                             |   compare
                          |          Screen 1           |
                          |                             |
                          |                             |
                          +-----------------------------+ Max. rows


See Also: Start address Overflow Max scan line

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