Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 91)

AN93
Rev. 1.3 91
5.7. U Registers
U registers (user-access registers) are 16-bit registers written by the AT:Uhh command and read by the AT:R (read
all U registers) command or AT:Rhh (read U-register hh) command. See the AT command list in Table 39 on
page 59. 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 can cause 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 also written and/or read in hexadecimal, but each bit or
combination of bits in the register represents an independent value. These individual bits are used to enable or
disable features and indicate states. Bits in these registers can be read/write, read only, reserved, or they may be
required to always be set to a certain value. 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 only 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 settings after a reset.
The U registers can be broken into three groups: call progress (U0–U33, U49–U4C), dialing (U37–U48), line
interface, and extended functions (U4D–UA9). Table 46 lists the available U registers, a brief description, and their
default values. Table 47 summarizes the signals and values available in the bit-mapped registers. Country-specific
register values are presented in "6.2. Country-Dependent Setup" on page 133. All default settings are chosen to
meet FCC requirements.
Table 46. U-Register Descriptions
Register Address
(Hex)
Name Description Default
Value
U00 0x0000 DT1A0 Dial-tone detection 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 detection 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 detection filters stage 3 biquad coefficients. 0x00A0
U0B 0x000B DT3B1 0x78B0
U0C 0x000C DT3B2 0xC305
U0D 0x000D DT3A2 0x4000
U0E 0x000E DT3A1 0xB50A