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PCD3349AP Datasheet(PDF) 7 Page - NXP Semiconductors |
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PCD3349AP Datasheet(HTML) 7 Page - NXP Semiconductors |
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7 / 20 page  1998 May 11 7 Philips Semiconductors Product specification 8-bit microcontroller with DTMF generator 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: ; 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. f f xtal 23 x 2 + () [] --------------------------------- = Table 3 DTMF standard frequencies and their implementation; value = LGF, HGF contents Table 4 Dialling symbols, corresponding DTMF frequency pairs and frequency registers content VALUE (HEX) FREQUENCY (Hz) DEVIATION 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 TELEPHONE KEYBOARD SYMBOLS DTMF FREQ. PAIRS (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 |
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