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82555 — Networking Silicon
16
Datasheet
4.2.4 Transmit Driver
The transmit differential lines are implemented with a digital slope controlled current driver that
meets the TP-PMD specifications. Current is sunk from the isolation transformer by the transmit
differential pins. The conceptual transmit differential waveform for 100 Mbps is illustrated in the
following figure.
The magnetics module that is external to the 82555 converts I
TDP
and I
TDN
to 2.0 V
pp
, as required
by the TP-PMD specification. The same magnetics used for 100BASE-TX mode should also work
in 10BASE-T mode. The following is a list of current magnetics modules available from several
vendors:
4.3 100BASE-TX Receive Blocks
The receive subsection of the 82555 accepts 100BASE-TX MLT-3 data on the receive differential
pair. Due to the advanced digital signal processing design techniques employed, the 82555 will
accurately receive valid data from Category 5 (CAT5) UTP and Type 1 STP cable of length well in
excess of 100 meters.
Figure 7. Conceptual Transmit Differential Waveform
(V
TDP
-V
TDN
)
+1V
0V
-1V
40mA
I
TDP
20mA
0
40mA
20mA
0
I
TDN
t
t
t
Table 3. Magnetics Modules
Vendor Model/Type 100BASE-TX 10BASE-T
Delta LF8200A Yes Yes
Pulse Engineering PE-68515 Yes Yes
Pulse Engineering H1012 Yes Yes