IP2022 Data Sheet www.ubicom.com 59 5.6.6 10base-T Ethernet Hardware To set up a SERDES unit for 10Base-T Ethernet, the input
data    from    a    differential    line    receiver    or    on-board
comparator is connected to the SxRXD input. The signals
designated Tx+, Tx-, TxD+, and TxD- correspond to the
SxTXP,   SxTXM,   SxTXPE,   and   SxTXME   pins   of   the
corresponding  serializers/deserializers.  These  pins  are
connected  to  an  RJ45  jack  through  a  transformer  with
terminations.   Figure   5-11   shows   an   example   circuit.
RTXPE,   RTXME,   RTXP,   RTXM   and   RL   values   vary
depending on the Ethernet magnetics used. Please refer
to  IP2022  Native  Ethernet  application  notes  for  more
details. For   10Base-T   Ethernet   operation,   each   SERDES   is
equipped with a squelch circuit for discriminating between
noise,   link   pulses,   and   data.   Link   pulses   are   sent
periodically  to  keep  the  channel  open  when  no  data  is
being transmitted. The squelch circuit handles link pulse
detection, link pulse polarity detection, carrier sense, and
EOP detection. Software The   SxMODE   register   must   be   programmed   for   a
recovered  clock,  and  the  PLL  clock  multiplier  must  be programmed  for  an  appropriate  speed.  For  example,  it
can be programmed to be 80 MHz for 8× oversampling.
The received data stream is used, together with the clock
recovery circuit, to recover the original transmit clock and
data. Note:  The  minimum  core  clock  frequency  required  in
10base-T mode is 80MHz. Software must perform the following functions: • Polarity detection and reversal. • Carrier sense. • Jabber detection. • Link integrity test and link pulse generation. • Random back off in case of collision. • When a collision is detected, sending a 32-bit jam se-
quence. Collisions can be detected by either receiv-
ing an RXXCRS interrupt or by setting the bit count to
7 and then received a RXBF interrupt while transmit-
ting. • Formation of Ethernet packet by putting the preamble,
sfd, destination address, source address, length/type,
MAC client data into the transmit buffer. Frame check
computation can be done in software or through the
LFSR units (see Section 5.9). • MAC layer functions. Figure 5-11  Ethernet Interface Example Clock recovery Rx+ Rx- Manchester decoding coding Serializer/Deserializer RJ45     Data
Encoder     Data
Decoder Manchester IP2022 Rtxpe Squelch SxRX- SxRX+ SxTXPE   Ethernet
Magnetics (LPF required) SxTXM SxTXME SxTXP TxD+ TxD- Tx- Tx+ Rtxme Rtxm Rtxp 515-064c.eps