70 www.ubicom.com IP2022 Data Sheet 5.6.12    SERDES Protocol-Specific Considerations UART Interface To set up a SERDES unit for UART mode, select UART
mode in  the  PRS3:0 bits of the SxMODE  register.  This
causes the data to be clocked in after a valid start bit is
detected.  Make  sure  that  the  polarity  selected  by  the
RPOREV bit in the SxRCFG register and the TPOREV bit
in the SxTCFG register match the polarity provided by the
RS-232  transceiver.  (Most  of  them  are  inverted.)  Make
sure the bit order is compatible with the data format (RS-
232  uses  LSB-first  bit  order).  The  receiver  uses  16X
oversampling, so select a clock divisor that is 16 times the
desired baud rate. To operate in UART mode, depending on the application,
either transmit or receive can be performed first. In both
cases, the configuration register needs to be programmed
with a bit count that is appropriate for the format. The bit
count depends on the number of data bits, stop bits, and
parity bits. The start bit is included in the bit count. The
receiver does not check for the presence of stop bits. To
detect   framing   errors   caused   by   missing   stop   bits,
increase the receiver’s bit count (i.e. the RXSCNT field in
the   SxRCFG   register)   and   test   the   trailing   bit(s)   in
software. SPI Protocol To set up a SERDES unit for the SPI protocol, set up the
clock with opposing phases for transmit and receive by
programming the SUBM1:0 field of the SxMODE register.
If in slave mode, specify an external clock. If in master
mode, specify an internal clock. In slave mode, software
must check if the designated slave select line is activated
before responding. In master mode, software must set the
designated  slave  select  pin  to  the  active  level  before
enabling the SERDES unit. To operate in SPI mode, once the transmit and receive bit
counts in the configuration registers are programmed with
non-zero   values,   the   SERDES   unit   begins   shifting
operations on the programmed clock edges. Caution must
be exercised to program them quickly to avoid losing any
data. USB 1.1 Protocol To set up a SERDES unit for USB mode, the received data
output  of  the  USB  transceiver  should  be  connected  to
SxRXD.  The  VP  and  VM  pins  of  the  transceiver  are
connected   to   the   SxRXP   and   SxRXM   pins   to   allow
detection  of  the  EOP  condition.  Figure  5-16  shows  the connections     required     between     an     external     USB
transceiver and the IP2022. Figure 5-16  USB Interface Example The SxMODE register must be programmed with values
for a recovered clock, and the PLL clock multiplier must be
programmed to generate the appropriate frequency. For
example, it can be programmed at 48 MHz for full speed
with  a  divisor  of  zero  (=1).  A  divisor  of  8  will  make  it
suitable  for  low-speed  operation.  The  synchronization
pattern must be programmed into the SxRSYNC register
to trigger an interrupt when a packet is received. To  operate  in  USB  mode,  software  must  perform  the
following functions: • CRC generation and checking. • Detecting reset of the device function, which is indi-
cated by 10 milliseconds of a single-ended zero (SE0)
condition on the bus. • Detecting  the  suspend  state,  which  is  indicated  by
more than 3 milliseconds of idle. Software must make
sure that the suspend current of 500 µA will be drawn
after 10 milliseconds of bus inactivity. • Formation of the USB packet by putting the sync, pid,
and  data  into  the  transmit  register  and  setting  the
proper count. 10Base-T Ethernet Protocol 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. PDIUSBP11A SxRXD IP2022 515-034.eps SxRXM SxTXP SxTXM D+ D- USB Bus SxRXP