
11-6
Graphics Controller Registers
`efmp69030 Databook
Revision 1.3 11/24/99
GR05
Graphics Mode Register
read/write at I/O address 3CFh with index at address 3CEh set to 05h
shared by both pipelines A and B
7
Reserved
6-5
Shift Register Control
In standard VGA modes, pixel data is transferred from the 4 graphics memory planes to the
palette via a set of 4 serial output bits. These 2 bits of this register control the format in
which data in the 4 memory planes is serialized for these transfers to the palette.
0, 0: One bit of data at a time from parallel bytes in each of the 4 memory planes is
transferred to the palette via the 4 serial output bits, with 1 of each of the serial output bits
corresponding to a memory plane. This provides a 4-bit value on each transfer for 1 pixel,
making possible a choice of 1 of 16 colors per pixel.
0, 1: Two bits of data at a time from parallel bytes in each of the 4 memory planes are
transferred to the palette in a pattern that alternates per byte between memory planes 0
and 2, and memory planes 1 and 3. First the even-numbered and odd-numbered bits of a
byte in memory plane 0 are transferred via serial output bits 0 and 1, respectively, while the
even-numbered and odd-numbered bits of a byte in memory plane 2 are transferred via
serial output bits 2 and 3. Next, the even-numbered and odd-numbered bits of a byte in
memory plane 1 are transferred via serial output bits 0 and 1, respectively, while the even-
numbered and odd-numbered bits of memory plane 3 are transferred via serial out bits 1
and 3. This provides a pair of 2-bit values (one 2-bit value for each of 2 pixels) on each
transfer, making possible a choice of 1 of 4 colors per pixel.
76543
210
A
&
B
Reserved
Shift Register Control
Odd/
Even
Read Mode
Reserved
Write Mode
Serial Out 1st Xfer 2nd Xfer 3rd Xfer 4th Xfer 5th Xfer 6th Xfer 7th Xfer 8th Xfer
Bit 3
plane 3
bit 7
plane 3
bit 6
plane 3
bit 5
plane 3
bit 4
plane 3
bit 3
plane 3
bit 2
plane 3
bit 1
plane 3
bit 0
Bit 2
plane 2
bit 7
plane 2
bit 6
plane 2
bit 5
plane 2
bit 4
plane 2
bit 3
plane 2
bit 2
plane 2
bit 1
plane 2
bit 0
Bit 1
plane 1
bit 7
plane 1
bit 6
plane 1
bit 5
plane 1
bit 4
plane 1
bit 3
plane 1
bit 2
plane 1
bit 1
plane 1
bit 0
Bit 0
plane 0
bit 7
plane 0
bit 6
plane 0
bit 5
plane 0
bit 4
plane 0
bit 3
plane 0
bit 2
plane 0
bit 1
plane 0
bit 0
Serial Out 1st Xfer 2nd Xfer 3rd Xfer 4th Xfer 5th Xfer 6th Xfer 7th Xfer 8th Xfer
Bit 3
plane 2
bit 7
plane 2
bit 5
plane 2
bit 3
plane 2
bit 1
plane 3
bit 7
plane 3
bit 5
plane 3
bit 3
plane 3
bit 1
Bit 2
plane 2
bit 6
plane 2
bit 4
plane 2
bit 2
plane 2
bit 0
plane 3
bit 6
plane 3
bit 4
plane 3
bit 2
plane 3
bit 0
Bit 1
plane 0
bit 7
plane 0
bit 5
plane 0
bit 3
plane 0
bit 1
plane 1
bit 7
plane 1
bit 5
plane 1
bit 3
plane 1
bit 1
Bit 0
plane 0
bit 6
plane 0
bit 4
plane 0
bit 2
plane 0
bit 0
plane 1
bit 6
plane 1
bit 4
plane 1
bit 2
plane 1
bit 0