Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 97)

AN93
Rev. 1.3 97
5.7.2. U00–U16 (Dial Tone Detect Filter Registers)
U00–U13 set the biquad filter coefficients for stages 1–4 of the dial-tone detection filter. U14, U15, and U16 set the
dial-tone detection 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,
two’s 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 "5.7.5. U34–U35 (Dial Tone Timing Register)" for more
information.
Table 48. U0–U16 (Dial Tone Registers)
Register Name Description Default
U00 DT1A0
Dial-tone detection filters stage 1 biquad coefficients.
0x0800
U01 DT1B1 0x0000
U02 DT1B2 0x0000
U03 DT1A2 0x0000
U04 DT1A1 0x0000
U05 DT2A0
Dial-tone detection filters stage 2 biquad coefficients.
0x00A0
U06 DT2B1 0x6EF1
U07 DT2B2 0xC4F4
U08 DT2A2 0xC000
U09 DT2A1 0x0000
U0A DT3A0
Dial-tone detection filters stage 3 biquad coefficients.
0x00A0
U0B DT3B1 0x78B0
U0C DT3B2 0xC305
U0D DT3A2 0x4000
U0E DT3A1 0xB50A
U0F DT4A0
Dial-tone detection filters stage 4 biquad coefficients.
0x0400
U10 DT4B1 0x70D2
U11 DT4B2 0xC830
U12 DT4A2 0x4000
U13 DT4A1 0x80E2
U14 DTK Dial-tone detection filter output scaler. 0x0009
U15 DTON Dial-tone detection ON threshold. 0x00A0
U16 DTOF Dial-tone detection OFF threshold. 0x0070