AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 106

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

Software Access
The Am79C976 controller implements the 256-byte
configuration space as defined by the PCI specification
revision 2.1. The 64-byte header includes all registers
required to identify the Am79C976 controller and its
function. Additionally, the optional PCI Power Manage-
ment Interface registers are implemented at location
44h - 4Bh. The layout of the Am79C976 PCI configura-
tion space is shown in Table 20.
The PCI configuration registers are accessible only by
configuration cycles. All multi-byte numeric fields follow
The Am79C976 controller supports mapping the ad-
dress space to both I/O and memory space. The value
in the PCI I/O Base Address register determines the
start address of the I/O address space. The register is
typically programmed by the PCI configuration utility
106
31
Base-Class
DATA_REG
MAX_LAT
Reserved
24
Subsystem ID
Device ID
Status
PMC
23
PMCSR_BSE
Header Type
Sub-Class
MIN_GNT
Reserved
Memory-Mapped I/O Base Address
Expansion ROM Base Address
Table 20.
I/O Base Address
16
P R E L I M I N A R Y
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
PCI Configuration Space Layout
Am79C976
15
Programming IF
NXT_ITM_PTR
Latency Timer
Interrupt Pin
Little Endian byte ordering. All write accesses to Re-
served locations have no effect; reads from these loca-
tions will return a data value of 0.
The Am79C976 controller requires 4K bytes of memory
address space for access to all the various internal reg-
isters as well as access to some setup information
stored in an external serial EEPROM. For compatibility
with previous PCnet family devices, the lower 32 bytes
of the register space are also mapped into I/O space,
but some functions of the Am79C976 controller (such
as network statistics) are only available in memory
space.
after system power-up. The PCI configuration utility
must also set the IOEN bit in the PCI Command register
to enable I/O accesses to the Am79C976 controller.
For memory mapped I/O access, the PCI Memory
Mapped I/O Base Address register controls the start
Subsystem Vendor ID
8
Command
Vendor ID
PMCSR
7
Cache Line Size
Interrupt Line
Revision ID
CAP-PTR
CAP_ID
0
Offset
0Ch
1Ch
2Ch
3Ch
FCh
00h
04h
08h
10h
14h
18h
20h
24h
28h
30h
34h
38h
40h
44h
48h
.
.
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