Specifications
AN93
70 Rev. 0.8
U17–U30 (Busy Tone Detect Filter Registers)
U17–U2A set the biquad filter coefficients for stages 1–
4 of the Busy Tone detect filter, and U2B, U2C, and U2D
set the Busy Tone detect output scalar, on threshold and
off threshold, respectively. (See Table 36.) The
thresholds are empirically found scalars and have no
units. These coefficients are programmed as 16-bit 2’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 values meet FCC
requirements.
U2E, U2F, and U30 set the busy cadence minimum total
time (BMTT), busy cadence delta time (BDLT), and
busy cadence minimum on time (BMOT), respectively.
Settings for busy cadences are specified as a range for
ON time (minimum ON and maximum ON) and a range
for OFF time (minimum OFF and maximum OFF). The
three values represented by BMTT, BDLT, and BMOT
fully specify these ranges. BMTT, minimum total time, is
equal to the minimum ON time plus the minimum OFF
time. BDLT (allowable delta) is equal to the maximum
total time (maximum ON time plus the maximum OFF
time) minus the minimum total time (BMTT). BMOT is
the minimum ON time. The values stored in the
registers are the hexadecimal representation of the
times in seconds multiplied by 7200. Default values
meet FCC requirements. See Figure 15 on page 73.
Table 36. U17–U30 (Busy Tone Detect Registers)
Register Name Description Default
U17 BT1A0 Busy tone detect filter stage 1 biquad coefficients. 0x0800
U18 BT1B1 0x0000
U19 BT1B2 0x0000
U1A BT1A2 0x0000
U1B BT1A1 0x0000
U1C BT2A0 Busy tone detect filter stage 2 biquad coefficients. 0x00A0
U1D BT2B1 0x6EF1
U1E BT2B2 0xC4F4
U1F BT2A2 0xC000
U20 BT2A1 0x0000
U21 BT3A0 Busy tone detect filter stage 3 biquad coefficients. 0x00A0
U22 BT3B1 0x78B0
U23 BT3B2 0xC305
U24 BT3A2 0x4000
U25 BT3A1 0xB50A
U26 BT4A0 Busy tone detect filter stage 4 biquad coefficients. 0x0400
U27 BT4B1 0x70D2
U28 BT4B2 0xC830
U29 BT4A2 0x4000
U2A BT4A1 0x80E2
U2B BTK Busy tone detect filter output scaler. 0x0009
U2C BTON Busy tone detect ON threshold. 0x00A0
U2D BTOF Busy tone detect OFF threshold. 0x0070
U2E BMTT Busy cadence minimum total time in seconds multiplied by 7200. 0x0870
U2F BDLT Busy cadence delta time in seconds multiplied by 7200. 0x25F8
U30 BMOT Busy cadence minimum on time in seconds multiplied by 7200. 0x0438