
Extension Registers
14-9
`efmp69030 Databook
Revision 1.3 11/24/99
XR0A
Frame Buffer Mapping Register
read/write at I/O address 3D7h with index at I/O address 3D6h set to 0Ah
shared by both pipelines A and B
7-6
Reserved
These bits always return the value of 0 when read.
5-4
Endian Byte Swapping Control
These 2 bits enable and select the type of byte-swapping performed on all word and
doubleword data written to and read from the graphics controller by the CPU as follows:
3
Reserved
This bit always returns the value of 0 when read.
2
Planar to Non-Planar Address Translation Enable
This bit provides a single-bit switch that can be used to alter the manner in which the frame
buffer memory appears from the perspective of the host bus to be organized so that it looks
as though the bits for each pixel are organized sequentially rather than in planes, even
though it may well still be organized in planes. This is done through a hardware-based
address translation scheme. The result is intended to be very similar to setting the frame
buffer memory to chain-4 mode using the graphics controller registers.
This switch is meant to be turned on occasionally as a convenience to programmers when
the graphics controller is being used in standard VGA modes, in order to allow a given
drawing operation or frame buffer save or restore operation to be carried out more easily.
Altering this bit has no effect on the settings in the graphics controller registers (the GRxx
series registers) that are normally used to specify the way in which the frame buffer memory
is organized. It is recommended, however, that bits 3 and 2 of the Miscellaneous Register
(GR06) be set so that the frame buffer memory is accessible using the A0000-AFFFF
memory space during the time that this feature is used.
0: Disables address translation in support of packed mode. This is the default after reset.
1: Enables address translation in support of packed mode.
76543
210
A
&
B
Reserved
(00)
Endian Byte Swapping
Control
(00)
Reserved
(0)
Planar to
Non X-late
(0)
Linear
Mapping
(0)
Paged
Mapping
(0)
Bits
5 4
Type of Endian Byte Swapping
0 0
No byte swapping. This is the default after reset.
0 1
Performs byte swapping wherein byte 0 is swapped with
byte 1 and byte 2 is swapped with byte 3.
1 0
Performs byte swapping wherein byte 0 is swapped with
byte 3 and byte 1 is swapped with byte 2.
1 1
Reserved