Silicon Laboratories ISOMODEM Si2401, Руководство пользователя

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Si2401
58 Preliminary Rev. 0.9
Reset settings = 0001_1001 (0x19)
SED (RVCZ). Ring Validation Control 2
Bit D7 D6 D5 D4 D3 D2 D1 D0
Name RAS[5:0]
Type R/W
Bit Name Function
7:6 Reserved Read returns zero.
5:0 RAS[5:0] Ring Assertion Time.
These bits set the minimum ring frequency for a valid ring signal. During ring qualification,
a timer is loaded with the RAS[5:0] field upon a TIP/RING event and decrements at a reg-
ular rate. If a second or subsequent TIP/RING event occurs after the timer has timed out,
the frequency of the ring is too low, and the ring is invalidated. The difference between
RAS[5:0] and RMX[5:0] identifies the minimum duration between TIP/RING events to qual-
ify as a ring, in binary-coded increments of 2.0 ms (nominal). A TIP/RING event typically
occurs twice per ring tone period. At 20 Hz, TIP/RING events would occur every
1/(2 x 20 Hz) = 25 ms. To calculate the correct RAS[5:0] value for a frequency range
[f_min, f_max], the following equation should be used: RAS[5:0] = 1 / (2 x f_min).