TNETX4090
ThunderSWITCH II 9-PORT 100-/1000-MBIT/S ETHERNET SWITCH
SPWS044E ± DECEMBER 1997 ± REVISED AUGUST 1999
pretagging and extended port awareness
The TNETX4090 can be incorporated into a hierarchical system, whereby this port is connected to a crossbar matrix with up to 17
DPretag on transmission ± containing the source port of the frame and a vector indicating the ports on the crossbar matrix for which the frame is destined.
DPretag on reception (learning format) ± containing the source port of the frame on the crossbar matrix.
DPretag on reception (directed format) ± containing a vector indicating the ports on this TNETX4090 for which the frame is destined.
The information contained within these tags also enables the TNETX4090 to be incorporated in a system where routing decisions are made at a higher level.
Use of pretagging is enabled by setting pretag in the appropriate PortxControl register.
pretag on transmission
Port 8 provides the frame source port and crossbar matrix destination port vector over eight cycles, beginning with the first cycle that M08_TXEN is high. The pretag takes the form of a
Figure 5 shows the timing relationship and Table 10 shows the fields within the tag.
M08_GTCLK
M08_TXEN
M08_TXD3± | 3±0 | 7±4 | 11±8 | 15±12 | 19±16 | 23±20 | 27±24 | 31±28 | Frame Data | |
M08_TXD0 | ||||||||||
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M08_TXD7± | 3±0 | 7±4 | 11±8 | 15±12 | 19±16 | 23±20 | 27±24 | 31±28 | Frame Data | |
M08_TXD4 | ||||||||||
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NOTE A: Ranges (e.g., 3±0) indicate which bits of the
Figure 5. Transmit Pretag Timing
38 | POST OFFICE BOX 655303 •DALLAS, TEXAS 75265 |
