vsc880 Vitesse Semiconductor Corp, vsc880 Datasheet - Page 18

• Manufacturer Part Number: vsc880
• Description: High Performance 16x16 Serial Crosspoint Switch Semiconductor Corporation
• Manufacturer: Vitesse Semiconductor Corp

High Performance 16x16
Serial Crosspoint Switch
Page 18
3.0 Cell Mode
3.1 Overview
VSC870 and the VSC880 switch in conjunction with a central (user defined) scheduler. In this mode, only fixed
length data packets (cells) can be supported. A cell clock is connected to the switch chip, and the switch chip
distributes the cell clock to all connected transceivers. The transceivers adjust their transmit cell clocks so that all
transceivers send the first word of a cell at such time that it arrives at the switch chip aligned to the switch cell clock
(see serial link operation above). In this mode, messages containing port card queue information are sent to the
central scheduler using an out of band control bus. Arbitration and flow control information are then sent back to the
port cards through the out of band control bus. The scheduler then configures the switch matrix by using the parallel
interface. A picture of a cell based system is shown below. Multiple switch chips can be used in parallel to increase
system bandwidth (see Application Note 32 “Design Guide for a Cell Based Switch with Central Control”).
3.2 Data Encoding Format
set to 00. Data words can have overhead bits 01, 10 or 11. The user can use these bits for signaling to the receiving
port card. Information such as start of frame and end of frame can be passed through the switch in this manner.
3.3 Receiver Operation
determine the word type. If the word is a command word sent from the port card, the switch will respond based on the
type of command specified in the C[4:0] bit field. If an IDLE word arrives at the end of the cell clock period and it
does not have an embedded cell clock, a cell clock error is flagged. If it is a data word, it is sent to the switch fabric
to be routed to its destination along with the user defined overhead bits.
In Cell Mode (CMODE = HIGH), a more sophisticated arbitration scheme can be supported by using the
The data word and command word formats are described in section 1.0. Command words use the overhead bits
If CMODE is HIGH, the receiver at each port examines the two overhead bits (B[1:0]) of the received word to
Port Card
Port Card
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Queuing
Queuing
System
System
Tel: (800) VITESSE • FAX: [phone] • Email: [e-mail]
VITESSE
SEMICONDUCTOR CORPORATION
VSC870
VSC870
Trans
Trans
Figure 8: Cell Based System
Internet: www.vitesse.com
Out-of-band Control Bus
Switch Card
VSC880
Switch
Chip
Scheduler/
Arbiter
Data Sheet
VSC880
G52191-0, Rev 4.2
01/05/01