CS8900 데이터 시트보기 (PDF) - Cirrus Logic

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CS8900

Highly-Integrated ISA Ethernet Controller

Cirrus Logic 

CS8900

tire packet has been received, the MAC validates

the FCS. If an error is detected, the CRCerror bit

(Register 4, RxEvent, Bit C) is set.

Enforcing Minimum Frame Size: The MAC

provides minimum frame size enforcement of

both transmit and receive packets. When the

TxPadDis bit (Register 9, TxCMD, Bit D) is

clear, transmit frames will be padded with addi-

tional bits to ensure that the receiving station

receives a legal frame (64 bytes, including

CRC). When TxPadDis is set, the CS8900 will

not add pad bits and will transmit frames less

that 64 bytes. If a frame is received that is less

than 64 bytes (including CRC), the Runt bit

(Register 4, RxEvent, Bit D) will be set indicat-

ing the arrival of an illegal frame.

Transmit Error Detection and Handling

The MAC engine monitors Ethernet activity and

reports and recovers from a number of error con-

ditions. For transmission, the MAC reports the

following errors in the TxEvent register (Register

8) and BufEvent register (Register C):

Loss of Carrier: Whenever the CS8900 is trans-

mitting on the AUI port, it expects to see its own

transmission "looped back" to its receiver. If it is

unable to monitor its transmission after the end

of the preamble, the MAC reports a loss-of-car-

rier error by setting the Loss-of-CRS bit

(Register 8, TxEvent, Bit 6). If the Loss-of-

CRSiE bit (Register 7, TxCFG, Bit 6) is set, the

host will be interrupted.

SQE Error: After the end of transmission on the

AUI port, the MAC expects to see a collision

within 64 bit times. If no collision is detected,

the SQEerror bit (Register 8, TxEvent, Bit 7) is

set. If the SQEerroriE bit is set (Register 7,

TxCFG, Bit 7), the host is interrupted. An SQE

error may indicate a fault on the AUI cable or a

faulty transceiver (it is assumed that the attached

transceiver supports this function).

Out-of-Window (Late) Collision: If a collision is

detected after the first 512 bits have been trans-

mitted, the MAC reports a late collision by

setting the Out-of-window bit (Register 8,

TxEvent, Bit 9). The MAC then forces a bad

CRC and terminates the transmission. If the Out-

of-windowiE bit (Register 7, TxCFG, Bit 9) is

set, the host is interrupted. A late collision may

indicate an illegal network configuration.

Jabber Error: If a transmission continues longer

than about 26 ms, the MAC disables the trans-

mitter and sets the Jabber bit (Register 8,

TxEvent, Bit A). The output of the transmitter

returns to idle and remains there until the host

issues a new Transmit Command. If the JabberiE

bit (Register 7, TxCFG, Bit A) is set, the host is

interrupted. A Jabber condition indicates that

there may be something wrong with the CS8900

transmit function. To prevent possible network

up to 7 bytes

1 byte

Packet

6 bytes

6 bytes

Frame

2 bytes

4 bytes

alternating 1s / 0s SFD DA

SA

Length Field LLC data Pad FCS

preamble

Direction of Transmission

frame length

min 64 bytes

max 1518 bytes

SFD = Start of Frame Delimiter

DA = Destination Address

SA = Source Address

Figure 3.6.

LLC = Logical Link Control

FCS = Frame Check Sequence (also

called Cyclic Redundancy Check, or CRC)

Ethernet Frame Format

26

DS150PP2

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