MSAN-216
Applications of the MDS108/MVTX1100
XLink Interface
Application Note
1.0
Purpose
DSxxxx
Issue 1
November 2002
Application note describing the XLink interface for the
MDS108 & MVTX1100 devices.
2.0
Scope
This document will cover clock requirements and
interface connections for the XLink interface. The
reader should be familiar with the MDS108/MVTX1100
datasheet before reading this application note.
than 200Mbps, the device must utilize a higher
frequency system clock in order to be able to support
the greater switching bandwidth requirements. With a
66MHz system clock (S_CLK) the device can support
full wire-speed forwarding on all 8 ports, and full wire
speed on the XLink port for expansion port data rates
up to 200Mbps. With an 80MHz system clock (S_CLK),
the device can support full wire-speed operation on all
8 ports and the XLink at data rates up to 400Mbps.
The XLink frequency of operation is determined by
strap options during power-up. The frame buffer
memory address pins L_A[10:9] provide the maximum
frequency of operation selection as shown in the
following table.
XLink Data
Rate
100Mbps
200Mbps
300Mbps
400Mbps
L_A[10:9]
Strap Level
11
10
01
00
3.0
Introduction
Port 8 on the MDS108/MVTX1100 is the XLink port.
The XLink port provides a high-speed communication
link between two chips. When cascaded via the XLink
port, two devices are capable of providing up to
sixteen 10/100Mbps ports.
When two devices are cascaded, the XLink port on
each device is treated as if it were a standard switch
output. Standard Ethernet packet protocols are
utilized, traditional packet integrity checks are
performed at the receiving XLink port, and standard
length Ethernet packets are transmitted.
4.0 XLink Speed and System Clock
Requirement
The XLink port utilizes an industry standard MII
interface. This XLink expansion port is capable of
operating at several data rates depending upon
configuration. Multiple data rates are achieved by
multiplying the MII reference clock for the XLink
interface (M8_REFCLK). When operating at greater
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