PCD3359A Datasheet, PDF (9/32 Pages) NXP Semiconductors – 8-bit microcontroller with DTMF generator and 128 bytes EEPROM

Philips Semiconductors
8-bit microcontroller with DTMF
generator and 128 bytes EEPROM
Product specification
PCD3359A
6.2 Melody output (P1.7/MDY)
The melody output (P1.7/MDY) is very useful for
generating musical notes when a purely sinusoidal signal
is not required, such as for ringer applications.
If bit EMO = 1 in the Melody and Port Interrupt Control
Register the TONE output is disabled (3-state) and a
square wave with the frequency defined by the HGF
contents is output on line P1.7/MDY. The square wave
(duty cycle = ¹²â„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 notes 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 (see equation in Section 6.3)
being 2 for the P1.7/MDY output, rather than 60 for the
TONE output. 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 25.
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 crystal frequency ‘f_xtal’ and the decimal value ‘x’ held
in the frequency registers (HGF and LGF). The variables
are related by the equation:
f = -_[---2---3-----₍-f--^x_x--^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.
1998 May 11
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