AM79C970A datasheet(25/219 Pages) AMD

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P R E L I M I N A R Y

AMD

Am79C970A

will be ignored except for the

SLEEP pin itself. Deasser-

tion of

SLEEP results in wake-up. The system must re-

frain from starting the network operations of the

PCnet-PCI II controller device for 0.5 s following the

deassertion of the

SLEEP signal in order to allow inter-

nal analog circuits to stabilize.

Both CLK and XTAL1 inputs must have valid clock sig-

nals present in order for the

SLEEP command to

take effect.

The

SLEEP pin should not be asserted during power

supply ramp-up. If it is desired that

SLEEP be asserted

at power up time, then the system must delay the asser-

tion of

SLEEP until three clock cycles after the comple-

tion of a hardware reset operation.

The

SLEEP pin must not be left unconnected. It should

be tied to VDD, if the power savings mode is not used.

XTAL1

Crystal Oscillator In

Input

The internal clock generator uses a 20 MHz crystal that

is attached to the pins XTAL1 and XTAL2. The network

data rate is one-half of the crystal frequency. XTAL1

may alternatively be driven using an external 20 MHz

CMOS level clock signal. Refer to the section “External

Crystal Characteristics” for more details.

Note that when the PCnet-PCI II controller is in coma

mode, there is an internal 22 k

Ω resistor from XTAL1 to

ground. If an external source drives XTAL1, some

power will be consumed driving this resistor. If XTAL1 is

driven LOW at this time power consumption will be mini-

mized. In this case, XTAL1 must remain active for at

least 30 cycles after the assertion of

SLEEP and

deassertion of

REQ.

XTAL2

Crystal Oscillator Out

Output

The internal clock generator uses a 20 MHz crystal that

is attached to the pins XTAL1 and XTAL2. The network

data rate is one-half of the crystal frequency. If an exter-

nal clock source is used on XTAL1, then XTAL 2 should

be left unconnected.

Microwire EEPROM Interface

EECS

EEPROM Chip Select

Output

This pin is designed to directly interface to a serial

EEPROM that uses the Microwire interface protocol.

EECS is connected to the Microwire EEPROM chip se-

lect pin. It is controlled by either the PCnet-PCI II con-

troller during command portions of a read of the entire

EEPROM, 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 Microwire interface protocol.

EEDI is connected to the Microwire EEPROM data input

pin. It is controlled by either the PCnet-PCI II controller

during command portions of a read of the entire

EEPROM, or indirectly by the host system by writing to

BCR19, bit 0.

Note that the EEDI pin is multiplexed with the

LNKST pin.

EEDO

EEPROM Data Out

Input

This pin is designed to directly interface to a serial

EEPROM that uses the Microwire interface protocol.

EEDO is connected to the Microwire EEPROM data out-

put pin. It is controlled by either the PCnet-PCI II control-

ler during command portions of a read of the entire

EEPROM, or indirectly by the host system by reading

from BCR19, bit 0.

Note that the EEDO pin is multiplexed with the

LED3

and SRD pins.

EESK

EEPROM Serial clock

Input/Output

This pin is designed to directly interface to a serial

EEPROM that uses the Microwire interface protocol.

EESK is connected to the Microwire EEPROM clock pin.

It is controlled by either the PCnet-PCI II controller di-

rectly during a read of the entire EEPROM, or indirectly

by the host system by writing to BCR19, bit 1.

Note that the EESK pin is multiplexed with the

LED1 and

SFBD pins.

The EESK pin is also used during EEPROM Auto-detec-

tion to determine whether or not an EEPROM is present

at the PCnet-PCI II controller Microwire interface. At the

rising edge of CLK during the last clock during which

RST is asserted, EESK is sampled to determine the

value of the EEDET bit in BCR19. A sampled HIGH

value means that an EEPROM is present, and EEDET

will be set to ONE. A sampled LOW value means that an

EEPROM is not present, and EEDET will be cleared to

ZERO. See the section “EEPROM Auto-Detection” 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 or-

der to resolve the EEDET setting.

AM79C970A Datasheet(PDF) 25 Page - Advanced Micro Devices

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