AM79C961A(1996) Ver la hoja de datos (PDF) - Advanced Micro Devices

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AM79C961A
(Rev.:1996)

PCnet™-ISA II Jumperless, Full Duplex Single-Chip Ethernet Controller for ISA

Advanced Micro Devices 

PRELIMINARY

56

Bits

Preamble

1010....1010

8

Bits

SYNCH

10101011

6

Bytes

Dest.

ADDR.

6

Bytes

Srce.

ADDR.

2

Bytes

Length

46–1500

Bytes

LLC

DATA

1–1500

Bytes

Pad

45–0

Bytes

4

Bytes

FCS

Start of Packet

at Time= 0

Bit

Bit Bit

Bit

0

70

7

Increasing Time

Most

Significant

Byte

Least

Significant

Byte

19364A-17

IEEE/ANSI 802.3 Frame and Length Field Transmission Order

Receive FCS Checking

Reception and checking of the received FCS is per-

formed automatically by the PCnet-ISA II controller.

Note that if the Automatic Pad Stripping feature is

enabled, the received FCS will be verified against the

value computed for the incoming bit stream including

pad characters, but it will not be passed to the host. If

a FCS error is detected, this will be reported by the

CRC bit in RMD1.

Receive Exception Conditions

Exception conditions for frame reception fall into two

distinct categories; those which are the result of normal

network operation, and those which occur due to

abnormal network and/or host related events.

Normal events which may occur and which are handled

autonomously by the PCnet-ISA II controller are basi-

cally collisions within the slot time and automatic runt

packet rejection. The PCnet-ISA II controller will ensure

that collisions which occur within 512 bit times from the

start of reception (excluding preamble) will be automat-

ically deleted from the receive FIFO with no host inter-

vention. The receive FIFO will delete any frame which

is composed of fewer than 64 bytes provided that the

Runt Packet Accept (RPA bit in CSR124) feature has

not been enabled. This criteria will be met regardless of

whether the receive frame was the first (or only) frame

in the FIFO or if the receive frame was queued behind

a previously received message.

Abnormal network conditions include:

s FCS errors

s Late collision

These should not occur on a correctly configured 802.3

network and will be reported if they do.

Host related receive exception conditions include

MISS, BUFF, and OFLO. These are described in the

Receive Descriptor section.

Am79C961A

83

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