SI3230 SILABS [Silicon Laboratories], SI3230 Datasheet - Page 27

• Manufacturer Part Number: SI3230
• Manufacturer: SILABS [Silicon Laboratories]

2.3.2. 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:
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.
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.
OSC2X
OSC1X
OSCnX
n
OSC2 = 0.49819 (2
OSC1
is the frequency to be generated;
=
=
=
oscillator
coeff
1
-- -
4
coeff
1
-- -
4
1
-- -
4
×
coeff
×
×
=
OSCn = coeff
2
0.50181
-------------------- -
1.49819
0.21556
-------------------- -
1.78434
1
----------------------- -
1
1 coeff
0.78434 2
=
n
–
+
=
= cos(2π f
coeff
cos
cos
OSCnY = 0,
OSC1Y = 0
OSC2Y = 0
circuit
⎛
⎝
×
⎛
⎝
×
2 π 1336
------------------- -
(
2 π 852
---------------- -
×
8000
8000
(
(
15
15
2
2
(
15
15
2
) = 16324 = 3FC4h
)
15
n
n
–
–
with
=
/8000 Hz),
⎞
⎠
x (2
–
⎞
⎠
1
1
25701
)
)
1
=
=
×
×
)
15
0.78434
×
0.49819
0.5
0.5
a
);
Desired V
------------------------------------ -
=
1.11 V
=
=
6465h
programmable
2370
1424
rms
Preliminary Rev. 0.96
=
=
rms
942h
590h
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
time the 16-bit counter will reset to zero and begin
counting until the inactive timer expires. The cadence
continues until the user clears the O1TAE and O1TIE
control bits. The zero crossing detect feature can be
implemented by setting the OZ1 bit (direct Register 32,
bit 5). This ensures that each oscillator pulse ends
without a dc component. The timing diagram in
Figure 12 is an example of an output cadence using the
zero crossing feature.
One-shot oscillation can be achieved by enabling O1E
and O1TAE. Direct control over the cadence can be
achieved by controlling the O1E bit (direct Register 32,
bit 2) directly if O1TAE and O1TIE are disabled.
The operation of tone generator 2 is identical to that of
tone generator 1 using its respective control registers.
Note: Tone Generator 2 should not be enabled simulta-
Continuous
waveforms may be created using tone generator 1 (not
available on tone generator 2) by setting the REL bit
(direct Register 32, bit 6), which enables reloading of
the OSC1, OSC1X, and OSC1Y registers at the
expiration of the active timer (OAT1).
neously with the ringing oscillator due to resource shar-
ing within the hardware.
phase
frequency-shift
Si3230
keying
(FSK)
27