PCI6421 datasheet(163/204 Pages) TI

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8−3

8.3

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 8−2 for a

complete description of the register contents.

Bit

Name

Command

Type

Default

Command

Offset:

04h

Type:

Read/Write, Read-only

Default:

0000h

Table 8−2. Command Register Description

BIT

FIELD NAME

TYPE

DESCRIPTION

15−11

RSVD

Reserved. Bits 15−11 return 0s when read.

INT_DISABLE

INTx disable. When set to 1, this bit disables the function from asserting interrupts on the INTx signals.

0 = INTx assertion is enabled (default)

1 = INTx assertion is disabled

FBB_ENB

Fast back-to-back enable. The SD host controller does not generate fast back-to-back transactions;

therefore, bit 9 returns 0 when read.

SERR_ENB

SERR enable. When bit 8 is set to 1, the SD host controller SERR driver is enabled. SERR can be

asserted after detecting an address parity error on the PCI bus.

STEP_ENB

Address/data stepping control. The SD host controller does not support address/data stepping;

therefore, bit 7 is hardwired to 0.

PERR_ENB

Parity error enable. When bit 6 is set to 1, the SD host controller is enabled to drive PERR response

to parity errors through the PERR signal.

VGA_ENB

VGA palette snoop enable. The SD host controller does not feature VGA palette snooping; therefore,

bit 5 returns 0 when read.

MWI_ENB

Memory write and invalidate enable. The SD host controller does not generate memory write invalidate

transactions; therefore, bit 4 returns 0 when read.

SPECIAL

Special cycle enable. The SD host controller does not respond to special cycle transactions; therefore,

bit 3 returns 0 when read.

MASTER_ENB

Bus master enable. When bit 2 is set to 1, the SD host controller is enabled to initiate cycles on the

PCI bus.

MEMORY_ENB

Memory response enable. Setting bit 1 to 1 enables the SD host controller to respond to memory cycles

on the PCI bus.

IO_ENB

I/O space enable. The SD host controller does not implement any I/O-mapped functionality; therefore,

bit 0 returns 0 when read.

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