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PCA148X Datasheet(PDF) 9 Page - NXP Semiconductors |
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PCA148X Datasheet(HTML) 9 Page - NXP Semiconductors |
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9 / 20 page  1998 Apr 21 9 Philips Semiconductors Product specification 32 kHz watch circuits with adaptive motor pulse PCA148x series Time calibration Taking a normal quartz crystal with frequency 32768kHz, frequency deviation ( ∆f/f) of ±15 × 10−6 and CL = 8.2 pF; the oscillator frequency is offset (by using non-symmetrical internal oscillator input and output capacitances of 10 pF and 15 pF) such that the frequency deviation is positive-only. This positive deviation can then be compensated for to maintain time-keeping accuracy. Once the positive frequency deviation is measured, a corresponding number ‘n’ (see Table 2) is programmed into the device’s EEPROM. This causes n pulses of frequency 8192 Hz to be inhibited every minute of operation, which achieves the required calibration. The programming circuit is shown in Fig.8. The required number n is programmed into EEPROM by varying VDD according to the steps shown in Fig.9, which are explained below: 1. The positive quartz frequency deviation ( ∆f/f) is measured, and the corresponding values of n are found according to Table 2. 2. VDD is increased to 5.1 V allowing the contents of the EEPROM to be checked from the motor pulse period tT3 at nominal frequency. 3. VDD is decreased to 2.5 V during a motor pulse to initialize a storing sequence. 4. The first VDD pulse to 5.1 V erases the contents of EEPROM. 5. When the EEPROM is erased a logic 1 is at the TEST pin. 6. VDD is increased to 5.1 V to read the data by pulsing VDD n times to 4.5 V. After the n edge, VDD is decreased to 2.5 V. 7. VDD is increased to 5.1 V to store n bits in the EEPROM. 8. VDD is decreased to 2.5 V to terminate the storing sequence and to return to operating mode. 9. VDD is increased to 5.1 V to check writing from the motor pulse period tT3. 10. VDD is decreased to the operation voltage between two motor pulses to return to operating mode. (Decreasing VDD during the motor pulse would restart the programming mode). The time calibration can be reprogrammed up to 100 times. Table 2 Quartz crystal frequency deviation, n and tT3 Notes 1. Increments of 2.03 × 10−6/step. 2. Increments of 122 µs/step. FREQUENCY DEVIATION ∆f/f ( × 10−6) NUMBER OF PULSES (n) tT3 (ms) 0(1) 0 31.250(2) +2.03 1 31.372 +4.06 2 31.494 .. . .. . .. . +127.89 63 38.936 Fig.8 Circuit for programming the time calibration. MSA971 VDD M1 M2 RESET VSS TEST OSC IN OSC OUT M PCA148x SERIES 1 2 3 4 8 7 6 5 32 kHz SIGNAL GENERATOR |
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