AM79C976 datasheet(99/309 Pages) AMD

99 / 309 page

8/01/00

Am79C976

P R E L I M INARY

Status, Receive Match, Receive Status, Magic Packet,

Transmit Status, and Start Frame/Byte Delimiter.

The LED pins can be configured to operate in either

open-drain mode (active low) or in totem-pole mode

(active high). The output can be stretched to allow the

human eye to recognize even short events that last only

several microseconds. After H_RESET, the four LED

outputs are configured as shown in Table 16.

For each LED register, each of the status signals is

AND’d with its enable signal, and these signals are all

OR’d together to form a combined status signal. Each

LED pin combined status signal can be programmed to

run to a pulse stretcher, which consists of a 3-bit shift

each shift register is normally at logic 0. The OR gate

output for each LED register asynchronously sets all

three bits of its shift register when the output becomes

asserted. The inverted output of each shift register is

used to control an LED pin. Thus, the pulse stretcher

provides 2 to 3 clocks of stretched LED output, or 52

ms to 78 ms. See Figure 4343.

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Power Savings Mode

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The Am79C976 controller supports power manage-

ment as defined in the PCI Bus Power Management In-

terface Specification V1.1 and Network Device Class

Power Management Reference Specification V1.0.

These specifications define the network device power

states, PCI power management interface including the

Capabilities Data Structure and power management

registers block definitions, power management events,

and OnNow network Wake-up events. In addition, the

Am79C976 controller supports legacy power manage-

ment schemes, such as Remote Wake-Up (RWU)

mode. The RWU mode can accommodate systems

that sleep with PCI bus power off or on and the PCI

clock running or stopped. The RWU pin can drive the

CPU's System Management Interrupt (SMI) line or a

system power controller.

The general scheme for the Am79C976 controller

power management is that when a wake-up event is

detected, a signal is generated to cause hardware ex-

ternal to the Am79C976 device to put the computer into

the working (S0) mode. The Am79C976 device sup-

ports three types of wake-up events:

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The Am79C976 device supports two types of wake-up

control mechanisms:

Table 16. LED Default Configuration

LED

Output

Indication

Driver Mode

Pulse Stretch

LED0

Link Status

Open Drain -

Active Low

Enabled

LED1

Activity

Open Drain -

Active Low

Enabled

LED2

Speed

Open Drain -

Active Low

Enabled

LED3

Coll

Open Drain -

Active Low

Enabled

COL

COLE

FDLS

FDLSE

LNKS

LNKSE

RCV

RCVE

RCVM

RCVME

XMT

XMTE

Pulse

Stretcher

MR_SPEED_SEL

100E

MPS

MPSE

22929B-45

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