VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC870

High Performance Serial

Backplane Transceiver

G52190-0, Rev 4.1

Page 13

01/05/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

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2.2.1 Packet Format

At both the transmit and receive sides, a start of packet is identified using a header word with TXTYP[1:0] and

RXTYP[1:0] set to “10”. Following this header word are the rest of the data words with TXTYP[1:0] and

RXTYP[1:0] set to “01”. This is shown in the table below.

Two general ways of transmitting a data packets are shown in the figure below. In the first example, when the

transceiver reads a CRQ word (which signals the start of a new packet) it waits for the ACK signal before

transmitting the header word. In the second example, the CRQ word is sent D words before the end of the packet in

order to utilize early arbitration and optimize the throughput. If there is no available packet for the next transmission,

a null CRQ word and a null header word are used as end of packet. Command words such as IDLEs can be

embedded inside the packet. On the receive side, the packets are delineated by the header word at the beginning and a

CRQ word at the end. The word sequence loaded into the VSC870 parallel interface is also shown in the figure below.

More details can be found in Application Note 31.

Figure 2: Packet Transmission Format

TXTYP[1:0]

RXTYP[1:0]

Transmit

B[1:0]

Receive

B[1:0]

Word Type

SCRAM = 1

SCRAM = 0

Error Check

0 0

0 0

0 0

Command Word

No Scramble

No Scramble

IDLE words

0 1

01 or 10

01,10,11

Data Word

Scramble

No Scramble

No

1 0

1 1

0 0

Header Word

No Scramble

No Scramble

No

1 1

0 0

0 0

Connection Request

No Scramble

No Scramble

No

11

CRQ

10

Header

01

D0

01

D1

01

DN

10

Header

01

D0

Example 1

Start of Packet

End of Packet

10

Header

01

D0

01

DN

11

CRQ

10

Header

01

D0

Example 2

Start of Packet

End of Packet

01

D(N-D)

D words before EOP

CRQ

CRQ

Start of Packet

Start of Packet