Specifications

AN93
Rev. 0.9 69
3.3.11. U-Registers
U-Registers (user-access registers) are 16-bit registers
directly written by the AT:Uhh command and read by the
AT:R (read all U-Registers) or AT:Rhh (read U-Register
hh) commands. See the AT command list in Table 18.
The U-Register number is the last two digits of the
register’s hexadecimal address. All values associated
with the U-Registers, the address, and the value written
to or read from the register are hexadecimal.
Some U-Registers are reserved and not available to the
user. Therefore, there are gaps in the available U-
Register address sequence. Additionally, some bits
within available U-Registers are reserved. Any attempt
to write to a non-listed U-Register or to write a reserved
bit to a value other than 0
b
causes unpredictable
modem operation.
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. Groups of bits in a bit-
mapped register can be used to represent a value. Bits
in these registers can be read/write, read only, reserved,
or they may be required to be set as a 1 or 0. Most
reserved bits return a 0 when read. Pay particular
attention when writing to bit-mapped registers to ensure
no reserved bits are overwritten. When changing bits in
a U-register with reserved bits, use a Read, Modify,
Write procedure. Read the register value with AT:R;
modify the desired bits, then write the new value with
AT:U. This will ensure the reserved bits are not altered.
All U-Registers revert to their default setting after a
reset.
The U-Registers can be broken into three groups: Call
Progress (U0–U33, U49–U4C), Dialing (U37–U48), and
Line Interface and Extended Functions (U4D–UA9).
Table 32 lists the available U-Registers, a brief
description, and their default values. Table 33
summarizes the signals and values available in the bit-
mapped registers.
Table 32. U-Register Descriptions
Register Address
(Hex)
Name Description Default
Value
U00 0x0000 DT1A0 Dial tone detect filters stage 1 biquad coefficients. 0x0800
U01 0x0001 DT1B1 0x0000
U02 0x0002 DT1B2 0x0000
U03 0x0003 DT1A2 0x0000
U04 0x0004 DT1A1 0x0000
U05 0x0005 DT2A0 Dial tone detect filters stage 2 biquad coefficients. 0x00A0
U06 0x0006 DT2B1 0x6EF1
U07 0x0007 DT2B2 0xC4F4
U08 0x0008 DT2A2 0xC000
U09 0x0009 DT2A1 0x0000
U0A 0x000A DT3A0 Dial tone detect filters stage 3 biquad coefficients. 0x00A0
U0B 0x000B DT3B1 0x78B0
U0C0x000CDT3B2 0xC305
U0D0x000DDT3A2 0x4000
U0E 0x000E DT3A1 0xB50A