AM79C90PC datasheet(18/62 Pages) AMD

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P R E L I M I N A R Y

Am79C90

Differences Between Ethernet Versions 1

and 2

a. Version 2 specifies that the collision detect of the

transceiver must be activated during the inter-

packet gap time.

b. Version 2 specifies some network management

functions, such as reporting the occurrence of colli-

sions, retries and deferrals.

c. Version 2 specifies that when transmission is ter-

minated, the differential transmit lines are driven to

0 volt differentially (half step).

Differences Between IEEE 802.3 and

Ethernet

a. IEEE 802.3 specifies a 2-byte length field rather

than a type field. The length field (802.3) describes

the actual amount of data in the frame.

b. IEEE 802.3 allows the use of a PAD field in the

data section of a frame, while Ethernet specifies

the minimum packet size at 64 bytes. The use of a

PAD allows the user to send and receive packets

which have less than 46 bytes of data.

A list of significant differences between Ethernet and

IEEE 802.3 at the physical layer include the following:

IEEE 802.3

Ethernet

End of Transmission

Half Step

Full Step (Rev 1)

State

Half Step (Rev 2)

Common Mode Voltage

±5.5 V

0 – +5 V

Common Mode Current Less than 1 mA

1.6 mA

±40%

Receive

±, Collision±

Input Threshold

±160 mV

±175 mV

Fault Protection

16 V

0 V

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