MDS212 Datasheet, PDF (38/111 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps Ethernet Switch

MDS212
Data Sheet
Signal Name
Source End
Target End
Description
X_DO[31:0]
X_DCLKO
X_DENO
X_FCI
X_DI[31:0]
X_DCLKI
X_DENI
X_FCO
32-bit-wide Transmit Data Bus - Includes an XPipe Message
Header and followed by the data payload.
Transmit Clock - Synchronous data clock provided by the source
end.
Transmit Data Enable - Provided by the source end to envelop the
entire XPipe message.
Flow Control Signal - A flow control pin from the target end to
signal the source end to active XON/XOFF.
Table 4 - Summary Description of the Source and Target End Signals
The Flow Control signal (X_FC) monitors the state of the receiving queue at the target end to prevent XPipe
message loss. When the target end does not have enough space to accommodate an entire XPipe message, the
target device sends a XOFF signal by driving the X_FCO signal to LOW. The source device will stop further
transmission until the X_FCI signal asserts the XON state, which is an active HIGH (See Table 4).
The XPipe Message Header provides the payload size, type of message, routing information, and control
information for the XPipe incoming message. The routing information includes the device ID and port ID. The
header size is dependent upon the message types and may be 2 to 4 words in length.
2-4 Words Header
XpipeFlow Message Header
0-64 Words Payload
Data Payload
Figure 8 - XPipe Message Header
8.2 XPipe Timing
The source device generates the X_CLKO signal to provide a synchronous transmit data clock. The Receiver will
then sample the data on the falling (negative) edge of the clock, as shown in Figure 9.
To identify the boundary between the XPipe messages and the data stream, the source device uses the X_DEN
signal to envelop the entire XPipe message. That is, a rising (positive) edge at the beginning of the first double word
(4 bytes) and a falling (negative) edge at the beginning of the last double word of an XPipe message as shown in
Figure 9.
Note: The negative edge does not occur at the end of the last double word, but instead, at the beginning of the last
double word. This allows XPipe messages to be sent consecutively (back-to-back).
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