IP2022 User’s Manual—Overview www.ubicom.com 9 on-chip   serializer/deserializer   (SERDES)   units.   These   units
support   popular   communication   protocols   such   as   10Base-T
Ethernet, GPSI, SPI, UART, and USB, allowing the IP2022 to be
used as a protocol converter in bridge and gateway applications. By performing data serialization and deserialization in hardware,
the CPU bandwidth needed to support serial communications is
greatly reduced, especially at high baud rates. Providing two units
allows  easy  implementation  of  protocol  conversion  or  bridging
functions, such as a USB-to-Ethernet bridge. 1.2.3 Low-Power Support Particular    attention    has    been    paid    to    minimizing    power
consumption. For example, an on-chip PLL allows use of a lower-
frequency external source (e.g., an inexpensive 2 MHz crystal can
be used to produce a 100 MHz on-chip clock), which reduces both
power consumption and EMI. In addition, software can change the
execution speed of the CPU to reduce power consumption, and a
mechanism is provided for automatically changing the speed on
entry  and  return  from  an  interrupt  service  routine.  The  speed
instruction  specifies  power-saving  modes  that  include  a  clock
divisor between 1 and 128. This divisor only affects the clock to the
CPU core, not the timers. The speed instruction also specifies
the  clock  source  (OSC1  clock,  RTCLK  oscillator,  or  PLL  clock
multiplier), and whether to disable the OSC1 clock oscillator or the
PLL.  The  speed  instruction  executes  using  the  current  clock
divisor.