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AM79C961KCW

PCnet™-ISA+ Jumperless Single-Chip Ethernet Controller for ISA

Advanced Micro Devices 

PRELIMINARY

AMD

FUNCTIONAL DESCRIPTION

The PCnet-ISA+ controller is a highly integrated system

solution for the PC-AT ISA architecture. It provides an

Ethernet controller, AUI port, and 10BASE-T trans-

ceiver. The PCnet-ISA+ controller can be directly

interfaced to an ISA system bus. The PCnet-ISA+ con-

troller contains an ISA bus interface unit, DMA Buffer

Management Unit, 802.3 Media Access Control func-

tion, separate 136-byte transmit and 128-byte receive

FIFOs, IEEE defined Attachment Unit Interface (AUI),

and Twisted-Pair Transceiver Media Attachment Unit.

In addition, a Sleep function has been incorporated

which provides low standby current for power sensitive

applications.

The PCnet-ISA+ controller is register compatible with

the LANCE (Am7990) Ethernet controller and

PCnet-ISA (Am79C960). The DMA Buffer Manage-

ment Unit supports the LANCE descriptor software

model and the PCnet-ISA+ controller is software com-

patible with the Novell NE2100 and NE1500T add-in

cards.

External remote boot PROMs and Ethernet physical ad-

dress PROMs are supported. The location of the I/O

registers, Ethernet address PROM, and the boot PROM

are determined by the programming of the registers in-

ternal to PCnet-ISA+. These registers are loaded at

RESET from the EEPROM.

Normally, the Ethernet physical address will be stored in

the EEPROM with the other configuration data. This re-

duces the parts count, board space requirements, and

power consumption. The option to use a standard paral-

lel 8 bit PROM is provided to manufactures who are

concerned about the non-volatile nature of EEPROMs.

The PCnet-ISA+ controller’s bus master architecture

brings to system manufacturers (adapter card and

motherboard makers alike) something they have not

been able to enjoy with other architectures—a low-cost

system solution that provides the lowest parts count and

highest performance. As a bus-mastering device, costly

and power-hungry external SRAMs are not needed for

packet buffering. This results in lower system cost due

to fewer components, less real-estate and less power.

The PCnet-ISA+ controller’s advanced bus mastering

architecture also provides high data throughput and low

CPU utilization for even better performance.

To offer greater flexibility, the PCnet-ISA+ controller has

a shared memory mode to meet varying application

needs. The shared memory architecture is compatible

with very low-end machines, such as PC/XTs that do not

support bus mastering, and very high end machines

which require local packet buffering for increased sys-

tem latency.

The network interface provides an Attachment Unit In-

terface and Twisted-Pair Transceiver functions. Only

one interface is active at any particular time. The AUI

allows for connection via isolation transformer to

10BASE5 and 10BASE2, thick and thin based coaxial

cables. The Twisted-Pair Transceiver interface allows

for connection of unshielded twisted-pair cables as

specified by the Section 14 supplement to IEEE 802.3

Standard (Type 10BASE-T).

Bus Master Mode

System Interface

The PCnet-ISA+ controller has two fundamental operat-

ing modes, Bus Master and Shared Memory. The

selection of either the Bus Master mode or the Shared

Memory mode must be done through hard wiring; it is

not software configurable. The Bus Master mode pro-

vides an Am7990 (LANCE) compatible Ethernet

controller, an Ethernet Address EEPROM or PROM, a

Boot PROM, and a set of device configuration registers.

The optional Boot PROM is in memory address space

and is expected to be 8–64K. On-chip address com-

parators control device selection based on the value of

the EEPROM.

The address PROM, board configuration registers, and

the Ethernet controller occupy 24 bytes of I/O space and

can be located on 16 different starting addresses.

Data buffers are located in system memory and can be

accessed by the PCnet-ISA+ controller when the device

becomes the Current Master.

Am79C961

1-503

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