am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 20

• Manufacturer Part Number: am79c970
• Description: Pcnettm-pci Single-chip Ethernet Controller For Pci Local Bus
• Manufacturer: Advanced Micro Devices

BASIC FUNCTIONS
System Bus Interface Function
The PCnet-PCI controller is designed to operate as a
Bus Master during normal operations. Some slave I/O
accesses to the PCnet-PCI controller are required in
normal operations as well. Initialization of the PCnet-
PCI controller is achieved through a combination of PCI
Configuration Space accesses, Bus Slave accesses,
Bus Master accesses and an optional read of a serial
EEPROM that is performed by the PCnet-PCI control-
ler. The EEPROM read operation is performed through
the Microwire interface. The ISO 8802-3 (IEEE/ANSI
802.3) Ethernet Address may reside within the serial
EEPROM. Some PCnet-PCI controller configuration
registers may also be programmed by the EEPROM
read operation.
The APROM, on-chip board-configuration registers,
and the Ethernet controller registers occupy 32-bytes of
I/O space which can be located on a wide variety of
starting addresses by modifying the Base Address Reg-
ister in the PCI Configuration Space.
Software Interface
The software interface to the PCnet-PCI controller is di-
vided into three parts. One part is the PCI configuration
registers. They are used to identify the PCnet-PCI con-
troller, and are also used to setup the configuration of
the device. The setup information includes the I/O base
address and the routing of the PCnet-PCI controller in-
terrupt channel. This allows for a jumperless
implementation.
The second portion of the software interface is the direct
access to the I/O resources of the PCnet-PCI controller.
The PCnet-PCI controller occupies 32-bytes of I/O
P R E L I M I N A R Y
Am79C970
space that must begin on a 32-byte block boundary. The
I/O base address can be changed to any 32-bit quantity
that begins on a 32-bit block boundary by modifying the
Base Address Register in the PCI Configuration Space.
The 32-byte I/O space is used by the software to pro-
gram the PCnet-PCI controller operating mode, to en-
able and disable various features, to monitor operating
status and to request particular functions to be executed
by the PCnet-PCI controller.
The third portion of the software interface is the descrip-
tor and buffer areas that are shared between the soft-
ware and the PCnet-PCI controller during normal
network operations. The descriptor area boundaries are
set by the software and do not change during normal
network operations. There is one descriptor area for re-
ceive activity and there is a separate area for transmit
activity. The descriptor space contains relocatable
pointers to the network packet data and it is used to
transfer packet status from the PCnet-PCI controller to
the software. The buffer areas are locations that hold
packet data for transmission or that accept packet data
that has been received.
Network Interfaces
The PCnet-PCI controller can be connected to an 802.3
network via one of two network interfaces. The Attach-
ment Unit Interface (AUI) provides an ISO 8802-3
(IEEE/ANSI 802.3) compliant differential interface to a
remote MAU or an on-board transceiver. The
10BASE-T interface provides a twisted-pair Ethernet
port. While in auto-selection mode, the interface in use
is determined by an auto-sensing mechanism which
checks the link status on the 10BASE-T port. If there is
no active link status, then the device assumes an AUI
connection.
AMD
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