Specifications

AN93
Rev. 0.9 75
3.3.12. U-Register Detailed Description
U-Registers are identified with the letter “U” followed by
the last two digits of the register’s hexadecimal address.
Values written to or read from these registers are in
hexadecimal format. Country-specific register values
are presented in "3.5.20. Country Dependent Setup" on
page 138. All default settings are chosen to meet FCC
requirements.
3.3.13. U00–U16 (Dial Tone Detect Filter Registers)
U00–U13 set the biquad filter coefficients for stages 1–4
of the Dial Tone detect filter, and U14, U15, and U16 set
the Dial Tone detect output scaler, on threshold and off
threshold, respectively.
The thresholds are empirically found scalars and have
no units. These coefficients are programmed as 16-bit
2s complement values. All A0 values are in 3.12 format
where 1.0 = 0x1000. All other coefficients are in 1.14
format where 1.0 = 0xC000. Default settings meet FCC
requirements. Additionally, register U34 sets the time
window in which a dial tone can be detected. Register
U35 sets the minimum time within the U34 window that
the dial tone must be present for a valid detection. See
"3.3.16. U34–U35 (Dial Tone Timing)" on page 79 for
more information.
Table 34. U0–U16 (Dial Tone Registers)
Register Name Description Default
U00 DT1A0 Dial tone detect filters stage 1 biquad coefficients. 0x0800
U01 DT1B1 0x0000
U02 DT1B2 0x0000
U03 DT1A2 0x0000
U04 DT1A1 0x0000
U05 DT2A0 Dial tone detect filters stage 2 biquad coefficients. 0x00A0
U06 DT2B1 0x6EF1
U07 DT2B2 0xC4F4
U08 DT2A2 0xC000
U09 DT2A1 0x0000
U0A DT3A0 Dial tone detect filters stage 3 biquad coefficients. 0x00A0
U0B DT3B1 0x78B0
U0C DT3B2 0xC305
U0D DT3A2 0x4000
U0E DT3A1 0xB50A
U0F DT4A0 Dial tone detect filters stage 4 biquad coefficients. 0x0400
U10 DT4B1 0x70D2
U11 DT4B2 0xC830
U12 DT4A2 0x4000
U13 DT4A1 0x80E2
U14 DTK Dial tone detect filter output scaler. 0x0009
U15 DTON Dial tone detect ON threshold. 0x00A0
U16 DTOF Dial tone detect OFF threshold. 0x0070