- Shift register (bits 6-5) 0 : Output the data in a straightforward serial fashion with each display plane output on its associated serial output. This is the standard VGA format. 1 : Output the data in a CGA-compatible 320-by-200, four-color graphics mode. This is used in display modes 4 and 5. 2 : Output the data eight bits at a time from the four bit planes. This is the format for the VGA mode 13h. - Odd/even mode (bit 4) This bit should be the complement of the O/E field in the Memory mode register.
0 : Normal VGA operating mode. 1 : Controls the VGA, so that even host addresses access even display planes (0,2) and odd host addresses access odd display planes (1,3).
- Read mode (bit 3) 0 : Select read mode #0. Data read from the VGA represents eight neighboring horizontal pixels in one display plane, as specified in the Read map select register. 1 : Select read mode #1. Data read from the VGA represents the result of a comparison made between the eight neighboring horizontal pixels from any or all display planes with the value in the Color compare register. The display planes selected for the comparison are determined in the Color don't care register.
- Write mode (bits 1-0)
b1 b0 Write mode 0 0 #0 (default) Direct write. See Data rotate, Set/reset, Enable set/reset, Bit mask registers. 0 1 #1 Used for fast 32-bit mem-to-mem MOVS. 1 0 #2 Color plane n (0-3) is filled with the value of bit n in the write data (Bit mask register). 1 1 #3 Uses (rotated) write data ANDed with Bit mask as bit mask. Uses set/reset as if set/reset were enabled for all planes.