PCD3351A datasheet(10/36 Pages) PHILIPS

10 / 36 page

1999 Oct 28

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers with DTMF generator

and 128 bytes EEPROM

PCA3351C; 52C; 53C;

PCD3351A; 52A; 53A

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.

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 4).

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 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 26.

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 from either HGF

or LGF is a function of the decimal value ‘x’ held in the

; where 60

≤ x ≤ 255 for TONE output.

6.4

DTMF frequencies

Assuming an oscillator frequency fxtal = 3.58 MHz, the

DTMF standard frequencies can be implemented as

shown in Table 7.

The relationships between telephone keyboard symbols,

DTMF frequency pairs and the frequency register contents

are given in Table 8.

Table 7

DTMF standard frequencies and their

implementation; value = LGF, HGF contents

Table 8

Dialling symbols, corresponding DTMF

frequency pairs and frequency register contents

xtal

23 x

()

[]

-----------------------------

VALUE

(HEX)

FREQUENCY (Hz)

DEVIATION

STANDARD

GENERATED

(%)

(Hz)

697

697.90

0.13

0.90

770

770.46

0.06

0.46

852

850.45

−0.18 −1.55

941

943.23

0.24

2.23

1209

1206.45

−0.21 −2.55

1336

1341.66

0.42

5.66

1477

1482.21

0.35

5.21

1633

1638.24

0.32

5.24

TELEPHONE

KEYBOARD

SYMBOLS

DTMF FREQ.

PAIRS

(Hz)

LGF

VALUE

(HEX)

HGF

VALUE

(HEX)

(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)

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