
SD Host Controller Programming Model
217
September 2005
SCPS110
12.3 Command Register
The command register provides control over the SD host controller interface to the PCI bus. All bit functions
adhere to the definitions in the PCI Local Bus Specification, as seen in the following bit descriptions. See
Table 122 for a complete description of the register contents.
Function 3 register offset: 04h
Register type:
Read/Write, Read-only
Default value:
0000h
BIT NUMBER
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESET STATE
0
Table 122. Command Register Description
BIT
FIELD NAME
TYPE
DESCRIPTION
1511
RSVD
R
Reserved. Bits 1511 return 00000b when read.
10
INT_DISABLE
RW
INTx disable. When set to 1b, this bit disables the function from asserting interrupts on the INTx signals.
0 = INTx assertion is enabled (default)
1 = INTx assertion is disabled
9
FBB_ENB
R
Fast back-to-back enable. The SD host controller does not generate fast back-to-back transactions;
therefore, bit 9 returns 0b when read.
8
SERR_ENB
RW
SERR enable. When bit 8 is set to 1b, the SD host controller SERR driver is enabled. SERR can be
asserted after detecting an address parity error on the PCI bus.
7
STEP_ENB
R
Address/data stepping control. The SD host controller does not support address/data stepping;
therefore, bit 7 is hardwired to 0b.
6
PERR_ENB
RW
Parity error enable. When bit 6 is set to 1b, the SD host controller is enabled to drive PERR response
to parity errors through the PERR signal.
5
VGA_ENB
R
VGA palette snoop enable. The SD host controller does not feature VGA palette snooping; therefore,
bit 5 returns 0b when read.
4
MWI_ENB
RW
Memory write and invalidate enable. The SD host controller does not generate memory write invalidate
transactions; therefore, bit 4 returns 0b when read.
3
SPECIAL
R
Special cycle enable. The SD host controller does not respond to special cycle transactions; therefore,
bit 3 returns 0b when read.
2
MASTER_ENB
RW
Bus master enable. When bit 2 is set to 1b, the SD host controller is enabled to initiate cycles on the
PCI bus.
1
MEMORY_ENB
RW
Memory response enable. Setting bit 1 to 1b enables the SD host controller to respond to memory
cycles on the PCI bus.
0
IO_ENB
R
I/O space enable. The SD host controller does not implement any I/O-mapped functionality; therefore,
bit 0 returns 0b when read.