PCD3349 查看數據表（PDF） - Philips Electronics
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PCD3349 Datasheet PDF : 20 Pages
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Philips Semiconductors
8-bit microcontroller with DTMF generator
Product specification
PCD3349A
6.2 Frequency registers
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:
f = -[---2---3-----(-f--xx--t-a-+--l---2----)---]--; where 60 ≤ x ≤ 255.
The frequency limitation given by x ≥ 60 is due to the
low-pass filters which would attenuate higher frequency
sine waves.
6.3 DTMF frequencies
Assuming an oscillator frequency fxtal = 3.58 MHz, the
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.
Table 3 DTMF standard frequencies and their
implementation; value = LGF, HGF contents
VALUE
FREQUENCY (Hz)
DEVIATION
(HEX) STANDARD GENERATED (%) (Hz)
DD
697
697.90
0.13 0.90
C8
770
770.46
0.06 0.46
B5
852
850.45 −0.18 −1.55
A3
941
943.23
0.24 2.23
7F
1209
1206.45 −0.21 −2.55
72
1336
1341.66
0.42 5.66
67
1477
1482.21
0.35 5.21
5D
1633
1638.24
0.32 5.24
Table 4 Dialling symbols, corresponding DTMF
frequency pairs and frequency registers content
TELEPHONE DTMF FREQ.
KEYBOARD PAIRS
SYMBOLS
(Hz)
LGF
VALUE
(HEX)
HGF
VALUE
(HEX)
0
(941, 1336)
A3
72
1
(697, 1209)
DD
7F
2
(697, 1336)
DD
72
3
(697, 1477)
DD
67
4
(770, 1209)
C8
7F
5
(770, 1336)
C8
72
6
(770, 1477)
C8
67
7
(852, 1209)
B5
7F
8
(852, 1336)
B5
72
9
(852, 1477)
B5
67
A
(697, 1633)
DD
5D
B
(770, 1633)
C8
5D
C
(852, 1633)
B5
5D
D
(941, 1633)
A3
5D
•
(941, 1209)
A3
7F
#
(941, 1477)
A3
67
1998 May 11
7
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