si2439-a-gm Silicon Laboratories, si2439-a-gm Datasheet - Page 54

• Manufacturer Part Number: si2439-a-gm
• Description: V.92 And V.34 Isomodem With Global Daa
• Manufacturer: Silicon Laboratories

Si2494/39
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 13 on page 46). 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 Si2494/39 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.
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