SI3201-FS datasheet(41/148 Pages) SILABS

41 / 148 page

Si3210/Si3211

Rev. 1.61

Figure 20. Simplified Tone Generator Diagram

2.3.2. Oscillator Frequency and Amplitude

Each of the two tone generators contains a two-pole

resonate

oscillator

circuit

with

programmable

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:

coeffn =cos(2fn/8000 Hz),

where fn is the frequency to be generated;

OSCn = coeffn x(2

15);

where desired Vrms is the amplitude to be generated;

OSCnY = 0,

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:

OSC1Y = 0

OSC2 = 0.49819 (215) = 16324 = 3FC4h

OSC2Y = 0

The above computed values 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.

2.3.3. 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 µs 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

OZn

OSSn

*Tone Generator 1 Only

n = "1" or "2" for Tone Generator 1 and 2, respectively

Two-Pole

Resonance

Oscillator

16-Bit

Modulo

Counter

OATn

OITn

OITnE

OATnE

OSCn

OSCnY

OSCnX

Load

Logic

Zero

Cross

Logic

Signal

Routing

OnSO

to TX Path

to RX Path

INT

Logic

OnIP

OnIE

INT

Logic

OnAP

OnAE

REL*

Load

Enable

8 kHz

Clock

Zero Cross

OnE

OAT

Expire

OIT

Expire

8 kHz

Clock

OSCnX

---

coeff

–

coeff

------------------------



–





Desired V

rms

1.11 V

rms

-------------------------------------



coeff

852

8000

-----------------





cos

0.78434

OSC1

0.78434 2



25701

6465h

OSC1X

---

0.21556

1.78434

---------------------



–





0.5



1424

590h

coeff

1336

8000

--------------------





cos

0.49819

OSC2X

---

0.50181

1.49819

---------------------



–





0.5



2370

942h

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