AM79C940VCW datasheet(27/122 Pages) AMD

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AMD

Am79C940

TMS, and TDI pins. SCLK must run for 5 cycles after the

assertion of

SLEEP. During the “Deep Sleep”, the SCLK

input can be optionally suspended for maximum power

savings. Upon exiting “Deep Sleep”, the hardware

RESET pin must be asserted and the SCLK restored.

The system must delay the setting of the bits in the MAC

configuration Control Register of the internal analog

circuits by 1 ns to allow for stabilization.

If the AWAKE bit is set prior to the activation of

SLEEP,

the 10BASE-T receiver and the

LNKST output pin re-

main operational.

If the RWAKE bit is set prior to

SLEEP being asserted,

the Manchester encoder/decoder, AUI and 10BASE-T

cells remain operational, as do the SRD, SRDCLK and

SF/BD outputs.

The input on XTAL1 must remain active for the AWAKE

or RWAKE features to operate. After exit from the Auto

Wake or Remote Wake modes, activation of hardware

RESET is not required when SLEEP is reasserted.

On deassertion of

SLEEP, the MACE device will go

through an internally generated hardware reset se-

quence, requiring re-initialization of MACE registers.

Power Supply

DVDD

Digital Power

There are four Digital VDD pins.

DVSS

Digital Ground

There are six Digital VSS pins.

AVDD

Analog Power

There are four analog VDD pins. Special attention

should be paid to the printed circuit board layout to avoid

excessive noise on the supply to the PLL in the

Manchester encoder/decoder (pins 66 and 83 in PLCC,

pins 67 and 88 in PQFP). These supply lines should be

kept separate from the DVDD lines as far back to the

power supply as is practically possible.

AVSS

Analog Ground

There are two analog VSS pins. Special attention

should be paid to the printed circuit board layout to avoid

excessive noise on the PLL supply in Manchester en-

coder/decoder (pin 73 in PLCC, pin 74 in PQFP). These

supply lines should be kept separate from the DVSS lines

as far back to the power supply as is practically possible.

PIN FUNCTIONS NOT AVAILABLE WITH

THE 80-PIN TQFP PACKAGE

In the 84-pin PLCC configuration,

ALL the pins are used

while in the 100-pin PQFP version, 16 pins are specified

as No Connects. Moving to the 80-pin TQFP configura-

tion requires the removal of 4 pins. Since Ethernet con-

trollers with integrated 10BASE-T have analog portions

which are very sensitive to noise, power and ground

pins are not deleted. The MACE device does have

several sets of media interfaces which typically go un-

used in most designs, however. Pins from some of

these interfaces are deleted instead. Removed are

the following:

s TXDAT– (previously used for the DAI interface)

s SRD (previously used for the EADI interface)

s DTV (previously used for the host interface)

s RXPOL (previously used as a receive frame

polarity LED driver)

Note that pins from four separate interfaces are re-

moved rather than removing all the pins from a single in-

terface. Each of these pins comes from one of the four

sides of the device. This is done to maintain symmetry,

thus avoiding bond out problems.

In general, the most critical of the four removed pins are

TXDAT– and SRD. Depending on the application, either

the DAI or the EADI interface may be important. In most

designs, however, this will not be the case.

PINS REMOVED AND THEIR EFFECTS

TXDAT–

The removal of TXDAT– means that the DAI interface is

no longer usable. The DAI interface was designed to be

used with media types that do not require DC isolation

between the MAU and the DTE. Media which do not

require DC isolation can be implemented more simply

using the DAI interface, rather than the AUI interface. In

most designs this is not a problem because most

media requires DC isolation (10BASE-T, 10BASE2,

10BASE5) and will use the AUI port. About the only me-

dia which does not require DC isolation is 10BASE-F.

SRD

The SRD pin is an output pin used by the MACE device

to transfer a receive data stream to external address

detection logic. It is part of the EADI interface. This pin is

used to help interface the MACE device to an external

CAM device. Use of an external CAM is typically re-

quired when an application will operate in promiscuous

mode and will need perfect filtering (i.e., the internal

hash filter will not suffice). Example applications for this

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