am79c972b Advanced Micro Devices, am79c972b Datasheet - Page 101

• Manufacturer Part Number: am79c972b
• Description: Pcnet?-fast+ Enhanced 10/100 Mbps Pci Ethernet Controller With Onnow Support
• Manufacturer: Advanced Micro Devices

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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
Am79C972 I/O resources in all of memory space. It is
located at offset 14h in the PCI Configuration Space.
Bit
31-5
4
MEMSIZE
RES
IOSPACE
Name
MEMBASE Memory mapped I/O base ad-
When the Am79C972 controller
is enabled for memory mapped
I/O mode (MEMEN is set), it mon-
itors the PCI bus for a valid mem-
ory command. If the value on
AD[31:5] during the address
phase of the cycles matches the
value
Am79C972 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 indicates the size of
the
Am79C972 controller requires.
When the host writes a value of
FFFF FFFFh to the Memory
Mapped I/O Base Address regis-
Reserved location. Read as zero;
write operations have no effect.
I/O space indicator. Read as one;
write operations have no effect.
Indicating that this base address
register describes an I/O base
address.
Description
dress most significant 27 bits.
These bits are written by the host
to specify the location of the
Am79C972 I/O resources in all of
memory space. MEMBASE must
be written with a valid address
before the Am79C972 controller
slave memory mapped I/O mode
is turned on by setting the ME-
MEN bit (PCI Command register,
bit 1).
Memory mapped I/O size re-
quirements. Read as zeros; write
operations have no effect.
memory
of
MEMBASE,
space
Am79C972
the
the
3
2-1
0
PCI Subsystem Vendor ID Register
Offset 2Ch
The PCI Subsystem Vendor ID register is a 16-bit reg-
ister that together with the PCI Subsystem ID uniquely
identifies the add-in card or subsystem the Am79C972
controller is used in. Subsystem Vendor IDs can be ob-
tained from the PCI SIG. A value of 0 (the default) indi-
cates that the Am79C972 controller does not support
subsystem identification. The PCI Subsystem Vendor
ID is an alias of BCR23, bits 15-0. It is programmable
through the EEPROM.
The PCI Subsystem Vendor ID register is located at off-
set 2Ch in the PCI Configuration Space. It is read only.
PCI Subsystem ID Register
Offset 2Eh
The PCI Subsystem ID register is a 16-bit register that
together with the PCI Subsystem Vendor ID uniquely
identifies the add-in card or subsystem the Am79C972
controller is used in. The value of the Subsystem ID is
up to the system vendor. A value of 0 (the default) indi-
cates that the Am79C972 controller does not support
subsystem identification. The PCI Subsystem ID is an
alias of BCR24, bits 15-0. It is programmable through
the EEPROM.
The PCI Subsystem ID register is located at offset 2Eh
in the PCI Configuration Space. It is read only.
MEMSPACE Memory space indicator. Read
PREFETCH Prefetchable. Read as zero; write
TYPE
ter, it will read back a value of 0 in
bit 4. That indicates a Am79C972
memory space requirement of 32
bytes.
operations have no effect. Indi-
cates that memory space con-
trolled by this base address
register is not prefetchable. Data
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.
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.
as zero; write operations have no
effect. Indicates that this base ad-
dress register describes a memo-
ry base address.
Memory type indicator. Read as
101