AM79C978A AMD [Advanced Micro Devices], AM79C978A Datasheet - Page 24

• Manufacturer Part Number: AM79C978A
• Description: Single-Chip 1/10 Mbps PCI Home Networking Controller
• Manufacturer: AMD [Advanced Micro Devices]

Board Interface
Note: Before programming the LED pins, see the
description of LEDPE in BCR2, bit 12.
LED0
LED0
This output is designed to directly drive an LED. By
default, LED0 indicates an active link connection. This
pin can also be programmed to indicate other network
status (see BCR4). The LED0 pin polarity is program-
mable, but by default it is active LOW. When the LED0
pin polarity is programmed to active LOW, the output
is an open drain driver. When the LED0 pin polarity is
programmed to active HIGH, the output is a totem
pole driver.
Note: The LED0 pin is multiplexed with the EEDI pin.
LED1
LED1
This output is designed to directly drive an LED. By de-
fault, LED1 indicates receive activity on the network.
This pin can also be programmed to indicate other net-
work status (see BCR5). The LED1 pin polarity is pro-
grammable, but by default, it is active LOW. When the
LED1 pin polarity is programmed to active LOW, the out-
put is an open drain driver. When the LED1 pin polarity
is programmed to active HIGH, the output is a totem pole
driver.
Note: The LED1 pin is multiplexed with the EESK pin.
The LED1 pin is also used during EEPROM Auto-
Detection to determine whether or not an EEPROM is
present at the Am79C978A controller interface. At the last
rising edge of CLK while RST is active LOW, LED1 is
sampled to determine the value of the EEDET bit in
BCR19. It is important to maintain adequate hold time
around the rising edge of the CLK at this time to ensure a
correctly sampled value. A sampled HIGH value means
that an EEPROM is present, and EEDET will be set to 1.
A sampled LOW value means that an EEPROM is not
present, and EEDET will be set to 0. See the EEPROM
Auto-Detection section for more details.
If no LED circuit is to be attached to this pin, then a pull-
up or pull-down resistor must be attached instead in
order to ground the EEDET setting.
WARNING: The input signal level of LED1 must be
insured for correct EEPROM detection before the
deassertion of RST.
LED2
LED2
This output is designed to directly drive an LED. This
pin can be programmed to indicate various network
24
Output
Output
Output
Am79C978A
status (see BCR6). The LED2 pin polarity is program-
mable, but by default it is active LOW. When the LED2
pin polarity is programmed to active LOW, the output
is an open drain driver. When the LED2 pin polarity is
programmed to active HIGH, the output is a totem
pole driver.
LED3
LED3
This output is designed to directly drive an LED. By de-
fault, LED3 indicates transmit activity on the network.
This pin can also be programmed to indicate other net-
work status (see BCR7). The LED3 pin polarity is pro-
grammable, but by default it is active LOW. When the
LED3 pin polarity is programmed to active LOW, the
output is an open drain driver. When the LED3 pin po-
larity is programmed to active HIGH, the output is a
totem pole driver.
Special attention must be given to the external circuitry
attached to this pin. When this pin is used to drive an
LED while an EEPROM is used in the system, then
buffering may be required between the LED3 pin and
the LED circuit. If an LED circuit were directly attached
to this pin, it may create an I
not be met by the serial EEPROM attached to this pin.
If no EEPROM is included in the system design or low
current LEDs are used, then the LED3 signal may be
directly connected to an LED without buffering. For
more details regarding LED connection, see the sec-
tion on LED Support.
Note: The LED3 pin is multiplexed with the EEDO pin.
LED4
LED4
This output is designed to directly drive an LED. This
pin can be programmed to indicate various network
status (see BCR48). The LED4 pin polarity is pro-
grammable, but by default it is active LOW. When the
LED4 pin polarity is programmed to active LOW, the
output is an open drain driver. When the LED4 pin po-
larity is programmed to active HIGH, the output is a
totem pole driver.
EEPROM Interface
EECS
EEPROM Chip Select
This pin is designed to directly interface to a serial
EEPROM that uses the 93C46 EEPROM interface
protocol. EECS is connected to the EEPROM’s chip
select pin. It is controlled by either the Am79C978A
controller during command portions of a read of the
entire EEPROM, or indirectly by the host system by
writing to BCR19, bit 2.
OL
requirement that could
Output
Output
Output