參數(shù)資料
型號(hào)： 935247300112
廠商： NXP SEMICONDUCTORS
元件分類(lèi)： 微控制器/微處理器
英文描述： 8-BIT, OTPROM, 16 MHz, MICROCONTROLLER, PDSO28
封裝： 7.50 MM, PLASTIC, SO-28
文件頁(yè)數(shù)： 35/35頁(yè)
文件大?。?/td> 243K
代理商： 935247300112
1997 Apr 16
9
Philips Semiconductors
Product specication
8-bit microcontrollers with DTMF generator,
8 kbytes OTP and 128 bytes EEPROM
PCD3755A; PCD3755E;
PCD3755F
6.2
Melody output (P1.7/MDY)
The melody output (P1.7/MDY) is very useful for
generating musical tones when a purely sinusoidal signal
is not required, such as for ringer applications.
The square wave (duty cycle = 12
23 or 52%) will include
the attenuated harmonics of the base frequency, which is
defined by the contents of the HGF register (Table 3).
However, even higher frequency tones may be produced
since the low-pass filtering on the TONE output is not
applied to the P1.7/MDY output. This results in the
minimum decimal value x in the HGF register being 2 for
the P1.7/MDY output, rather than 60 for the TONE output
- the value shown in equation (1). A sinusoidal TONE
output is produced at the same time as the melody square
wave, but due to the filtering, the higher frequency sine
waves with x < 60 will not appear at the TONE output.
Since the melody output is shared with P1.7, the port
flip-flop of P1.7 has to be set HIGH before using the
melody output. This is to avoid conflicts between melody
and port outputs. The melody output drive depends on the
configuration of port P1.7/MDY; see Chapter 14, Table 24.
6.3
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 ‘f’ is dependent
on the clock frequency ‘fxtal’ and the decimal value ‘x’ held
in the frequency registers (HGF and LGF). The variables
are related by the equation:
(1)
The frequency limitation given by x
≥ 60 is due to the
low-pass filters which would attenuate higher frequency
sine waves.
f
xtal
23 x
2
+
()
[]
---------------------------------
=
where
60
x
255
≤≤
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