Specifications

Si2493
Rev. 1.3 45
6. User-Access Registers
(U-Registers)
U-Registers are 16-bit registers written by the AT:Uaa
command and read by the AT:R (read all U-Registers)
or AT:Raa (read U-Register aa) commands (see the AT
command list in Table 11 on page 37). Many aspects of
the modem’s and DAA’s behavior can be enabled/
disabled, configured, monitored, and/or modified
through U-Registers; however, most of them will not be
needed in normal use.
There are two types of U-Registers. The first represents
a single 16-bit term, such as a filter coefficient,
threshold, delay, or other quantity. These registers can
be read from or written to as a single 16-bit value. The
second type of U-Register is bit-mapped. Bit-mapped
registers are written and/or read in hexadecimal, but
each bit or combination of bits in the register represents
an independent value or status information. These
individual bits are used to enable or disable features
and indicate states.
Some U-Registers are reserved and not available to the
user. Therefore, there are gaps in the available U-
Register address map. Additionally, some bits within
available U-Registers are reserved. Any attempt to write
a non-zero value to a reserved U-Register or bit may
cause unpredictable modem operation.
With over 100 U-Registers, the Si2493 offers an
unprecedented level of programmability for a controller-
based modem. A detailed list of these registers and
their use is beyond the scope of this data sheet. Refer
to “AN93: ISOmodem
®
Chipset Family Designer’s
Guide” for details.