Silicon Laboratories Si2404, Manual

Page: 107 / 307

AN93
Rev. 1.4 107
Example: The United States specifies a busy tone “on” time from 450 to 550 ms and “off” time from 450 to 550 ms.
Thus the minimum “on” and “off” times are 0.45 s each , and the maximum “on” and “off” times are 0.55 s each.
 The busy cadence minimum on time is 0.45 s, thus BMOT = 0.45 x 7200 = 0x0CA8.
 The busy cadence minimum total time is 0.45 s + 0.45 s = 0.9 s, thus BMTT = 0.9 x 7200 = 6480 = 0x1950.
 The maximum total time is 0.55 s + 0.55 s = 1.1 s, thus BDLT = (1.1 – 0.9) x 7200 = 1440 = 0x05A0.
The hexadecimal values are stored in the appropriate registers using the AT:Uhh command. Detection parameters
can be wider than the minimum specifications. This is often done in the modem defaults and other suggested
settings so that one set of parameters can cover a broad number of different country requirements.
Register U1D9 defines the number of Busy Tone cadences (on/off) that the modem must detect before reporting
the BUSY message. The actual cadence count is the value of U1D9 plus 1. The default value of U1D9 is 3. Thus,
by default, the modem reports BUSY every four busy cadences.
The busy tone detector is configured using registers U17–U30 as described in "5.7.3. U17–U30 (Busy Tone Detect
Filter Registers)" on page 105.
Figure 27. Cadence Timing
K — — — — 0x0005
400/440
A0 0x0020 0x0200 0x0400 0x0040 —
B1 0x7448 0x7802 0x73D5 0x75A7 —
B2 0xC0F6 0xC0CB 0xC2A4 0xC26B —
A2 0x4000 0x4000 0x4000 0x4000 —
A1 0x96AB 0x8359 0x8D93 0x85C1 —
K — — — — 0x0008
Table 61. BPF Biquad Values (Continued)
BPF Biquad
Values
Stage 1 Stage 2 Stage 3 Stage 4 Output Scalar
Maximum Cadence
TOTAL Time
Minimum Cadence
TOTAL Time
(BMTT)
(RMTT)
Cadence Delta
Time (BDLT)
(RDLT)
Minimum ON Time
(BMOT)
(RMOT)