pcd3349a NXP Semiconductors, pcd3349a Datasheet - Page 7

• Manufacturer Part Number: pcd3349a
• Description: 8-bit Microcontroller With Dtmf Generator
• Manufacturer: NXP Semiconductors

Philips Semiconductors
6.2
The two frequency registers HGF and LGF define two
frequencies. From these, the digital sine synthesizers
together with the Digital-to-Analog Converters (DACs)
construct two sine waves. Their amplitudes are precisely
scaled according to the bandgap voltage reference. This
ensures TONE output levels independent of supply
voltage and temperature. The amplitude of the Low Group
Frequency sine wave is attenuated by 2 dB compared to
the amplitude of the High Group Frequency sine wave.
The two sine waves are summed and then filtered by an
on-chip switched capacitor and RC low-pass filters. These
guarantee that all DTMF tones generated fulfil the CEPT
recommendations with respect to amplitude, frequency
deviation, total harmonic distortion and suppression of
unwanted frequency components.
The value 00H in a frequency register stops the
corresponding digital sine synthesizer. If both frequency
registers contain 00H, the whole frequency generator is
shut off, resulting in lower power consumption.
The frequency of the sine wave generated is dependent
upon the decimal value ‘x’ held in the frequency registers
(HGF and LGF), and this may be calculated as follows:
The frequency limitation given by x
low-pass filters which would attenuate higher frequency
sine waves.
6.3
Assuming an oscillator frequency f
DTMF standard frequencies can be implemented as
shown in Table 3.
The relationship between telephone keyboard symbols
and the frequency register contents are given in Table 4.
1998 May 11
f
=
8-bit microcontroller with DTMF generator
-------------------------------- -
23 x
Frequency registers
DTMF frequencies
f
xtal
+
2
; where 60
x
255.
xtal
60 is due to the
= 3.58 MHz, the
7
Table 3 DTMF standard frequencies and their
Table 4 Dialling symbols, corresponding DTMF
TELEPHONE
VALUE
KEYBOARD
(HEX)
SYMBOLS
DD
C8
B5
A3
5D
7F
72
67
C
D
A
B
0
1
2
3
4
5
6
7
8
9
#
implementation; value = LGF, HGF contents
frequency pairs and frequency registers content
STANDARD
1209
1336
1477
1633
FREQUENCY (Hz)
697
770
852
941
DTMF FREQ.
(941, 1336)
(697, 1209)
(697, 1336)
(697, 1477)
(770, 1209)
(770, 1336)
(770, 1477)
(852, 1209)
(852, 1336)
(852, 1477)
(697, 1633)
(770, 1633)
(852, 1633)
(941, 1633)
(941, 1209)
(941, 1477)
PAIRS
(Hz)
GENERATED
1206.45
1341.66
1482.21
1638.24
697.90
770.46
850.45
943.23
VALUE
(HEX)
LGF
DD
DD
DD
DD
A3
C8
C8
C8
B5
B5
B5
C8
B5
A3
A3
A3
Product specification
PCD3349A
(%)
0.13
0.06
0.18
0.24
0.21
0.42
0.35
0.32
DEVIATION
VALUE
(HEX)
HGF
5D
5D
5D
5D
7F
7F
7F
7F
72
72
67
72
67
72
67
67
(Hz)
0.90
0.46
1.55
2.23
2.55
5.66
5.21
5.24