Specifications

AN93
Rev. 0.8 73
Example: The United States specifies a busy tone with
on time from 450 to 550 ms and off time from 450 to
550 ms. Thus, minimum ON time equals 0.450 s,
maximum ON time equals 0.550 s, minimum OFF time
equals 0.450 sec, and maximum OFF time equals
0.550 sec. Busy Cadence Minimum Total
Time = 0.450 s + 0.450 s = 0.900 s. Therefore,
BMTT = (0.900)(7200)d = 0x1950. Maximum total
time = 0.550 s + 0.550 s = 1100 ms, so BDLT = (1.10–
0.900)(7200)d = 0x05A0, and
BMOT = (0.450)(7200)d = 0x0CA8. The hexadecimal
values are stored in the appropriate registers using the
AT:Uaa command where aa is the U-Register number
(hexadecimal address). 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 large
number of different country requirements.
Figure 15. Cadence Timing
U31–U33 (Ringback Cadence Registers)
U31, U32, and U33 set the ringback cadence minimum
total time (RMTT), ringback cadence delta time (RDLT),
and ringback cadence minimum on time (RMOT). (See
Table 38.) Country-specific settings for ringback
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 RMTT, RDLT, and RMOT fully
specify these ranges. RMTT, minimum total time, is
equal to the minimum ON time plus the minimum OFF
time. RDLT (allowable delta) is equal to the maximum
total time (maximum ON time plus the maximum OFF
time) minus the minimum total time (RMTT). RMOT 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.
U34–U35 (Dial Tone Timing)
U34 determines the period of time the modem attempts
to detect a dial tone. U35 sets the time within this
window the dial tone must be present in order to return
a valid dial tone detection. The value stored in U35 is
the hexadecimal representation of the time in seconds
multiplied by 7200. The value in U34 is the hexadecimal
representation of the time in seconds multiplied by
1000. The time window represented in U34 must be
larger than the dial tone present time represented in
register U35. (See Table 39.)
Maximum Cadence
TOTAL Time
Minimum Cadence
TOTAL Time
(BMTT)
(RMTT)
Cadence Delta
Time
(BDLT)
(RDLT)
Minimum ON Time
(BMOT)
(RMOT)
Table 38. Ringback Cadence Registers
Register Name Description Default
U31 RMTT Ringback cadence minimum total time in seconds multiplied by 7200. 0x4650
U32 RDLT Ringback cadence delta in seconds multiplied by 7200. 0xEF10
U33 RMOT Ringback cadence minimum on time in seconds multiplied by 7200. 0x1200