SI3211 ETC, SI3211 Datasheet - Page 31

• Manufacturer Part Number: SI3211
• Description: PROSLIC PROGRAMMABLE CMOS SLIC/CODEC WITH RINGING/BATTERY VOLTAGE GENERATION
• Manufacturer: ETC

Oscillator Frequency and Amplitude
Each of the two tone generators contains a two-pole
resonate
frequency and amplitude, which are programmed via
indirect registers OSC1, OSC1X, OSC1Y, OSC2,
OSC2X, and OSC2Y. The sample rate for the two
oscillators is 8000 Hz. The equations are as follows:
where f
where desired Vrms is the amplitude to be generated;
n = 1 or 2 for oscillator 1 or oscillator 2, respectively.
For example, in order to generate a DTMF digit of 8, the
two required tones are 852 Hz and 1336 Hz. Assuming
the generation of half-scale values (ignoring twist) is
desired, the following values are calculated:
OSC1X
OSCnX
n
OSC1
is the frequency to be generated;
=
oscillator
Counter
=
coeff
Modulo
1
-- -
4
16-Bit
*Tone G enerator 1 O nly
n = "1" or "2" for Tone Generator 1 and 2, respectively
8 kHz
OAT n
Clock
coeff
OITn
1
-- -
4
=
OSCn = coeff
1
0.21556
-------------------- -
1.78434
0.78434 2
n
1 coeff
----------------------- -
1
=
O ATnE
= cos(2 f
–
+
O ITnE
cos
OSCnY = 0,
coeff
OSC1Y = 0
circuit


2 852
---------------- -
Expire
Expire
8000
OA T
OIT
2
15
OnE
15
2
Figure 18. Simplified Tone Generator Diagram
n
n
15
–
with
=
/8000 Hz),


1
–
25701
(2
Cross
=
Logic
Zero
1
15
Logic
Logic
0.5
0.78434
INT
INT
a
);
Desired V
--------------------------------------- -
=
=
OZn
1.11 V
6465h
programmable
1424
Zero Cross
O SSn
Logic
O nAE
Load
O nAP
O nIE
OnIP
RMS
=
Preliminary Rev. 1.11
RMS
590h
REL*
R egister
Enable
Load
Resonance
The computed values above would be written to the
corresponding registers to initialize the oscillators. Once
the oscillators are initialized, the oscillator control
registers can be accessed to enable the oscillators and
direct their outputs.
Tone Generator Cadence Programming
Each of the two tone generators contains two timers,
one for setting the active period and one for setting the
inactive period. The oscillator signal is generated during
the active period and suspended during the inactive
period. Both the active and inactive periods can be
programmed from 0 to 8 seconds in 125 s steps. The
active period time interval is set using OAT1 (direct
registers 36 and 37) for tone generator 1 and OAT2
(direct registers 40 and 41) for tone generator 2.
To enable automatic cadence for tone generator 1,
define the OAT1 and OIT1 registers and then set the
O1TAE bit (direct Register 32, bit 4) and O1TIE bit
(direct Register 32, bit 3). This enables each of the
timers to control the state of the Oscillator Enable bit,
O1E (direct Register 32, bit 2). The 16-bit counter will
begin counting until the active timer expires, at which
Two-Pole
Oscillator
8 kHz
Clock
OSC2X
O SCnX
O SCnY
Si3210/Si3211/Si3212
O SCn
OSC2 = 0.49819 (2
=
coeff
1
-- -
4
2
0.50181
---------------------
1.49819
=
cos
OSC2Y = 0
Routing


Signal
2 1336
--------------------
8000
2
15
15
) = 16324 = 3FC4h
–
O nSO
1


=
0.5
0.49819
=
to RX Path
to TX Path
2370
=
942h
31