IP2022 User’s Manual—Peripherals www.ubicom.com 287 4.6.12    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