AM79C975VCW datasheet(118/304 Pages) AMD

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118

Am79C973/Am79C975

P R E L I M INARY

will drive DEVSEL indicating it

will respond to the access.

IOBASE is read and written by

the host. IOBASE is cleared by

H_RESET and is not affected by

S_RESET or by setting the STOP

bit.

4-2

IOSIZE

I/O size requirements. Read as

zeros; write operations have no

effect.

IOSIZE indicates the size of the

I/O

space

the

Am79C973/

Am79C975 controller requires.

When the host writes a value of

FFFF FFFFh to the I/O Base Ad-

dress register, it will read back a

value of 0 in bits 4-2. That indi-

cates an Am79C973/Am79C975

I/O space requirement of 32

bytes.

RES

Reserved location. Read as zero;

write operations have no effect.

IOSPACE

I/O space indicator. Read as one;

write operations have no effect.

Indicating that this base address

address.

PCI Memory Mapped I/O Base Address Register

Offset 14h

The PCI Memory Mapped I/O Base Address register is

a 32-bit register that determines the location of the

Am79C973/Am79C975 I/O resources in all of memory

space. It is located at offset 14h in the PCI Configuration

Space.

Bit

Name

Description

31-5

MEMBASE Memory mapped I/O base ad-

dress most significant 27 bits.

These bits are written by the host

to specify the location of the

Am79C973/Am79C975 I/O re-

sources in all of memory space.

MEMBASE must be written with a

valid

address

before

the

Am79C973/Am79C975 controller

slave memory mapped I/O mode

is turned on by setting the ME-

MEN bit (PCI Command register,

bit 1).

When

the

Am79C973/

Am79C975 controller is enabled

for memory mapped

I/O mode

(MEMEN is set), it monitors the

PCI bus for a valid memory com-

mand. If the value on AD[31:5]

during the address phase of the

cycles matches the value of

MEMBASE,

the

Am79C973/

Am79C975 controller will drive

DEVSEL indicating it will respond

to the access.

MEMBASE is read and written by

the host. MEMBASE is cleared

by H_RESET and is not affected

by S_RESET or by setting the

STOP bit.

MEMSIZE

Memory mapped I/O size re-

quirements. Read as zeros; write

operations have no effect.

MEMSIZE indicates the size of

the

memory

space

the

Am79C973/Am79C975 controller

requires. When the host writes a

value of FFFF FFFFh to the

Memory Mapped I/O Base Ad-

dress register, it will read back a

value of 0 in bit 4. That indicates

a Am79C973/Am79C975 memo-

ry space requirement of 32 bytes.

PREFETCH Prefetchable. Read as zero; write

operations have no effect. Indi-

cates that memory space con-

trolled by this base address

in the memory mapped I/O space

cannot be prefetched. Because

one of the I/O resources in this

address space is a Reset regis-

ter, the order of the read access-

es is important.

2-1

TYPE

Memory type indicator. Read as

zeros; write operations have no

effect. Indicates that this base ad-

dress register is 32 bits wide and

mapping can be done anywhere

in the 32-bit memory space.

MEMSPACE Memory space indicator. Read

as zero; write operations have no

effect. Indicates that this base ad-

dress register describes a memo-

ry base address.

AM79C975VCW Datasheet(PDF) 118 Page - Advanced Micro Devices

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