AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 32

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

System Bus Interface
The Am79C976 controller is designed to operate as a
bus master during normal operations. Some slave I/O
accesses to the Am79C976 controller are required in
nor mal operations as well. Initialization of the
Am79C976 controller is achieved through a combina-
tion of PCI Configuration Space accesses, bus slave
accesses, bus master accesses, and an optional read
of a ser ial EEPROM that is perfor med by the
Am79C976 controller. The EEPROM read operation is
performed through the 93Cxx EEPROM interface. The
ISO 8802-3 (IEEE/ANSI 802.3) Ethernet Address may
reside within the serial EEPROM. Some Am79C976
controller configuration registers may also be pro-
grammed by the EEPROM read operation.
The Am79C976 controller requires 4 Kbytes 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. The location of the memory or I/O address
space claimed by this device is programmed through
the base address registers in PCI configuration space.
For diskless stations, the Am79C976 controller sup-
ports a ROM or Flash-based (both referred to as the
Expansion ROM throughout this specification) boot de-
vice of up to 16 Mbyte in size. The host can map the
boot device to any memory address that aligns to a de-
vice size boundary by modifying the Expansion ROM
Base Address register in the PCI configuration space.
The Expansion ROM device size is determined by the
value set in the ROM-CFG register.
Software Interface
The software interface to the Am79C976 controller is
divided into three parts. One part is the PCI configura-
32
P R E L I M I N A R Y
Am79C976
tion registers used to identify the Am79C976 controller
and to setup the configuration of the device. The setup
information includes the I/O or memory mapped I/O
base address, mapping of the Expansion ROM, and
the routing of the Am79C976 controller interrupt chan-
nel. This allows for a jumperless implementation.
The second portion of the software interface is the
direct access to the I/O resources of the Am79C976
controller. The Am79C976 controller requires 4 Kbytes
of memory address space for access to all the various
internal registers as well as access to some setup infor-
mation stored in an external serial EEPROM. For com-
patibility 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 mem-
ory space.
The third portion of the software interface is the de-
scriptor and buffer areas that are shared between the
software and the Am79C976 controller during normal
network operations. The descriptor area boundaries
are set by the software and do not change during nor-
mal network operations. There is one descriptor area
for receive activity and there is a separate area for
transmit activity. The descriptor space contains relocat-
able pointers to the network frame data, and it is used
to transfer frame status from the Am79C976 controller
to the software. The buffer areas are locations that hold
frame data for transmission or that accept frame data
that has been received.
Network Interface
The Am79C976 controller can be connected to an
IEEE 802.3 or proprietary network through the IEEE
802.3-compliant Media Independent Interface (MII).
The MII is a nibble-wide interface to an external
100-Mbps and/or 10-Mbps transceiver device.
The Am79C976 controller supports both half-duplex
and full-duplex operation on the network interface.
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