VITESSE

SEMICONDUCTOR CORPORATION

Data Sheet

VSC880

High Performance 16x16

Serial Crosspoint Switch

G52191-0, Rev 4.2

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

Internet: www.vitesse.com

2.0 Packet Mode

2.1 Overview

In Packet Mode (CMODE=LOW), command words can be sent through the transceiver to the switch chip

requesting connection to one or multiple output channels. Acknowledge (ACK) information will be returned to the

transceiver from the switch allowing the port card to start transmitting data. In this mode of operation, no controller

chip is connected to the switch chip as the switch chip handles all arbitration for connection requests. Details on how

the transceiver operates in Packet Mode mode can be found in the VSC870 data sheet and the applications note 31:

“Design Guide for a Packet Based Switch with Distributed Control”. A picture of a self routing system is shown

below. The minimum packet size in this mode of operation is 4 words or 16 bytes.

Figure 6: Packet Mode System

2.2 Data Encoding Format

The data word and command word formats are described in section 1.0. In this section the header word and

Connection Request (CRQ) word format at the serial input and serial output of the switch are described.

2.2.1 Header word Format on the Serial Data Lines

The header word format as seen at the serial output of the transceiver or switch chip is shown below. Two

overhead bits are added to designate a header word to the receiving chip. The serial data is transmitted with the MSB

first.

If multiple headers are sent in a row, the VSC870 will convert all but the first one into IDLEs.

Port Card

Trans

RXFIFO

TXFIFO

Port Card

Trans

RXFIFO

TXFIFO

Switch

Chip

Switch Card

VSC870

VSC870

VSC880