grammed to active HIGH, the output is a totem pole
driver.
larity is programmed to active HIGH, the output is a
totem pole driver.
Note: The LED0 pin is multiplexed with the EEDI pin.
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 IOL requirement that could
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.
LED1
LED1
Output
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
output is an open drain driver. When the LED1 pin po-
larity is programmed to active HIGH, the output is a
totem pole driver.
Note: The LED3 pin is multiplexed with the EEDO pin.
Note: The LED1 pin is multiplexed with the EESK pin.
LED4
The LED1 pin is also used during EEPROM Auto-
Detection to determine whether or not an EEPROM is
present at the Am79C978 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 EE-
PROM is not present, and EEDET will be set to 0. See
the EEPROM Auto-Detection section for more details.
LED4
Output
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 program-
mable, 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 polarity is pro-
grammed to active HIGH, the output is a totem pole
driver.
EEPROM Interface
EECS
If no LED circuit is to be attached to this pin, then a pull-
up or pull-down resistor must be attached in order to
select the EEDET setting.
EEPROM Chip Select
Output
This pin is designed to directly interface to a serial EE-
PROM that uses the 93C46 EEPROM interface proto-
col. EECS is connected to the EEPROM’s chip select
pin. It is controlled by either the Am79C978 controller
during command portions of a read of the entire EE-
PROM, or indirectly by the host system by writing to
BCR19, bit 2.
WARNING: The input signal level of LED1 must be in-
sured for correct EEPROM detection before the deas-
sertion of RST.
LED2
LED2
Output
EEDI
This output is designed to directly drive an LED. This
pin can be programmed to indicate various network
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 pro-
grammed to active HIGH, the output is a totem pole
driver.
EEPROM Data In
Output
This pin is designed to directly interface to a serial
EEPROM that uses the 93C46 EEPROM interface pro-
tocol. EEDI is connected to the EEPROM’s data input
pin. It is controlled by either the Am79C978 controller
during command portions of a read of the entire
EEPROM, or indirectly by the host system by writing to
BCR19, bit 0.
LED3
Note: The EEDI pin is multiplexed with the LED0 pin.
LED3
Output
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-
EEDO
EEPROM Data Out
Input
This pin is designed to directly interface to a serial
EEPROM that uses the 93C46 EEPROM interface pro-
tocol. EEDO is connected to the EEPROM’s data out-
put pin. It is controlled by either the Am79C978
Am79C978
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