AM79C978 Advanced Micro Devices, AM79C978 Datasheet - Page 87

• Manufacturer Part Number: AM79C978
• Description: Single-Chip 1/10 Mbps PCI Home Networking Controller
• Manufacturer: Advanced Micro Devices

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 five
LED outputs are configured as shown in Table 17.
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
register clocked at 38 Hz (26 ms). The data input of
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 45.
Power Savings Mode
Power Management Support
The controller supports power management as defined
in the PCI Bus Power Management Interface Specifica-
tion V1.1 and Network Device Class Power Manage-
m e n t R e f e r e n c e S p e c i f i c a t i o n V 1 . 0 a . T h e s e
specifications define the network device power states,
PCI power management interface including the Capa-
bilities Data Structure and power management regis-
ters block definitions, power management events, and
OnNow network wake-up events.
The general scheme for the Am79C978 power man-
agement is that when a PCI wake-up event is detected,
a signal is generated to cause hardware external to the
Am79C978 device to put the computer into the working
(S0) mode.
Output
LED0
LED1
LED2
LED3
LED4
LED
Table 17. LED Default Configuration
Link Status
Indication
Transmit
Receive
Speed
Status
Power
Status
Driver Mode
Open Drain -
Open Drain -
Open Drain -
Open Drain -
Open Drain -
Active Low
Active Low
Active Low
Active Low
Active Low
Pulse Stretch
Enabled
Enabled
Enabled
Enabled
Enabled
Am79C978
The Am79C978 device supports three types of wake-
up events:
1. Magic Packet Detect
2. OnNow Pattern Match Detect
3. Link State Change
Figure 46 shows the relationship between these wake-
up events and the various outputs used to signal to the
external hardware.
OnNow Wake-Up Sequence
The system software enables the PME pin by setting
the PME_EN bit in the PMCSR register (PCI configura-
tion registers, offset 44h, bit 8) to 1. When a wake-up
event is detected, the controller sets the PME_STATUS
bit in the PMCSR register (PCI configuration registers,
offset 44h, bit 15). Setting this bit causes the PME sig-
nal to be asserted. Assertion of the PME signal causes
external hardware to wake up the CPU. The system
software then reads the PMCSR register of every PCI
device in the system to determine which device as-
serted the PME signal.
When the software determines that the signal came
from the controller, it writes to the device's PMCSR to
put the device into power state D0. The software then
writes a 0 to the PME_STATUS bit to clear the bit and
turn off the PME signal, and it calls the device's soft-
ware driver to tell it that the device is now in state D0.
The system software can clear the PME_STATUS bit
either before, after, or at the same time that it puts the
device back into the D0 state.
MR_SPEED_SEL
POWERE
RCVME
POWER
FDLSE
LNKSE
RCVM
RCVE
MPSE
COLE
XMTE
LNKS
FDLS
100E
MPS
COL
RCV
XMT
Figure 45. LED Control Logic
22206B-49
Pulse
Stretcher
To
87