AM79C971 Datasheet, PDF (29/265 Pages) Advanced Micro Devices – PCnet™-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus

BASIC FUNCTIONS
System Bus Interface
The Am79C971 controller is designed to operate as a
bus master during normal operations. Some slave I/O
accesses to the Am79C971 controller are required in
normal operations as well. Initialization of the
Am79C971 controller is achieved through a combina-
tion of PCI Configuration Space accesses, bus slave
accesses, bus master accesses, and an optional read
of a serial EEPROM that is performed by the
Am79C971 controller. The EEPROM read operation is
performed through the 93C46 EEPROM interface. The
ISO 8802-3 (IEEE/ANSI 802.3) Ethernet Address may
reside within the serial EEPROM. Some Am79C971
controller configuration registers may also be pro-
grammed by the EEPROM read operation.
The Address PROM, on-chip board-configuration reg-
isters, and the Ethernet controller registers occupy 32
bytes of address space. I/O and memory mapped I/O
accesses are supported. Base Address registers in the
PCI configuration space allow locating the address
space on a wide variety of starting addresses.
For diskless stations, the Am79C971 controller sup-
ports a ROM or Flash-based (both referred to as the
Expansion ROM throughout this specification) boot de-
vice of up to 1 Mbyte in size. The host can map the boot
device to any memory address that aligns to a 1-Mbyte
boundary by modifying the Expansion ROM Base Ad-
dress register in the PCI configuration space.
Software Interface
The software interface to the Am79C971 controller is
divided into three parts. One part is the PCI configura-
tion registers used to identify the Am79C971 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 Am79C971 controller interrupt chan-
nel. This allows for a jumperless implementation.
The second portion of the software interface is the di-
rect access to the I/O resources of the Am79C971 con-
troller. The Am79C971 controller occupies 32 bytes of
address space that must begin on a 32-byte block
boundary. The address space can be mapped into I/O
or memory space (memory mapped I/O). The I/O Base
Address Register in the PCI Configuration Space con-
trols the start address of the address space if it is
mapped to I/O space. The Memory Mapped I/O
Base Address Register controls the start address of
the address space if it is mapped to memory space.
The 32-byte address space is used by the software to
program the Am79C971 controller operating mode, to
enable and disable various features, to monitor operat-
ing status, and to request particular functions to be ex-
ecuted by the Am79C971 controller.
The third portion of the software interface is the de-
scriptor and buffer areas that are shared between the
software and the Am79C971 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 Am79C971 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 Interfaces
The Am79C971 controller can be connected to an
IEEE 802.3 or proprietary network via one of four net-
work interfaces. The Media Independent Interface (MII)
provides an IEEE 802.3-compliant nibble-wide inter-
face to an external 100- and/or 10-Mbps transceiver
device. The Attachment Unit Interface (AUI) provides
an ISO 8802-3 (IEEE/ANSI 802.3) defined differential
interface. On-board MAU and or off-board MAU con-
nection with or without an AUI cable is supported. The
10BASE-T interface provides a twisted-pair Ethernet
port, which is ISO 8802-3 (IEEE/ANSI 802.3)-compli-
ant, and contains the auto-negotiation capability, which
is IEEE 802.3u-compliant. The General Purpose Serial
Interface (GPSI) allows bypassing the Manchester
Encoder/Decoder (MENDEC) and is functionally equiv-
alent to the GPSI found on the LANCE.
While in auto-selection mode, the interface in use is de-
termined by the Network Port Manager. If the quiescent
state of the MII MDIO pin is HIGH, the MII is activated.
If the MII MDIO pin is LOW, the Am79C971 device
checks the link status on the 10BASE-T port. If the
10BASE-T link status is good, the 10BASE-T port is se-
lected. If there is no active link status, then the device
assumes an AUI connection. The 10BASE-T port will
continue to monitor the link status while the AUI is ac-
tive. The software driver can override this automatic
configuration at anytime by disabling the auto-selection
and forcing a network port to be attached to the internal
MAC. The GPSI port can only be enabled by disabling
the auto-selection and manually selecting the GPSI as
the network port.
The Am79C971 controller supports half-duplex and
full-duplex operation on all four network interfaces (i.e.,
AUI, 10BASE-T, GPSI, and MII).
Am79C971
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