IP2022 Data Sheet www.ubicom.com 71 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. Figure 5-17  Ethernet Interface Example The SxRXP and SxRXM signals must not be allowed to
float, even if they are not used. These signals must not be
driven low simultaneously. 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 also must be done in software. • MAC layer functions. GPSI Interface GPSI   is   a   general-purpose,   point-to-point,   full-duplex
serial bus protocol. Only two devices are allowed to exist
on  a  bus.  The  GPSI  master  device  is  responsible  for
maintaining   bus   timing   by   driving   two   continuously
running clocks, TxClk and RxClk. The device that does not drive the clocks is the slave device. The TxEn and TxD
signals are synchronized to the TxClk clock. The RxD and
RxEn signals are synchronized to the RxClk clock. The
mapping of GPSI signals to SERDES signals is shown in
Table 5-11. COLLISION is connected to a general-purpose port pin,
and  TxBUSY  is  connected  to  the  SxTXME  to  provide
additional flow control capabilities for the software device
driver. The COLLISION signal is used to indicate that a
PHY device has detected a collision condition. This signal
is only useful when the SERDES is connected to a PHY
device or acting as a PHY device. The TxBUSY signal is used by a GPSI device to indicate
that the device is currently busy, and that another device
should  not  attempt  to start  a  data  transfer.  COLLISION
and TxBUSY are asynchronous to both TxClk and RxClk.
TxBUSY can be configured as either an input or an output
depending which device is slower and has a need to stall
incoming data. Clock recovery      Analog
Components Magnetics 515-064.eps Tx Rx+
Rx- Manchester decoding coding Serializer/Deserializer +
- RJ45    Data
Endoder    Data
Decoder Manchester IP2022       Table 5-11  GPSI Interface Signal Usage
GPSI Signal Name SERDES Signal Name Direc- tion Description TxClk SxTXM I/O Transmit clock TxD SxTXP Output Transmit data TxEn SxTXPE Output Transmit data valid RxClk SxCLK I/O Receive clock RxD SxRXD Input Receive data RxEn SxRXP Input Receive data valid COLLSION    GPIO I/O Indicates a collision
at PHY layer (han-
dled by software) TxBUSY SxTxME I/O Indicates a data
transfer in progress
(handled by soft-
ware)