AM79C978VCSLASHW datasheet(29/261 Pages) AMD

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Am79C978

grammed to active HIGH, the output is a totem pole

driver.

Note: The LED0 pin is multiplexed with the EEDI pin.

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 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 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.

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.

WARNING: The input signal level of LED1 must be in-

sured for correct EEPROM detection before the deas-

sertion of RST.

LED2

Output

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.

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-

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 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.

Note: The LED3 pin is multiplexed with the EEDO pin.

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

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.

EEDI

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.

Note: The EEDI pin is multiplexed with the LED0 pin.

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

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