PCA2002CX8SLASH5SLASH1 datasheet(7/25 Pages) NXP

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PCA2002_5

Product data sheet

Rev. 05 — 11 November 2008

7 of 25

NXP Semiconductors

PCA2002

32 kHz watch circuit programmable output period and pulse width

7.6 Programming procedure

To ensure that the oscillator starts up correctly you must execute a reset sequence (see

Figure 4).

For a watch it is essential that the timing calibration can be made after the watch is fully

assembled. In this situation, the supply pins are often the only terminals which are still

accessible.

Writing to the OTP cells and performing the related functional checks is achieved in the

PCA2002 by modulating the supply voltage. The necessary control circuit consists

basically of a voltage level detector, an instruction counter which determines the function

to be performed, and an 8-bit shift register which allows writing the OTP cells of an 8-bit

word in one step and which acts as data pointer for checking the OTP content.

• State 1; measurement of the crystal oscillator frequency (divided by 1024)

• State 2; measurement of the inhibition time

• State 3; write/check word A

• State 4; write/check word B

• State 5; check word C (don’t care since no meaning)

• State 6; check word D (type recognition)

Each instruction state is switched on with a pulse to VP(prog)(start). After this large pulse, an

initial waiting time of t0 is required. The programming instructions are then entered by

modulating the supply voltage with small pulses (amplitude VP(mod) and pulse width tmod).

The ﬁrst small pulse deﬁnes the start time, the following pulses perform three different

functions, depending on the time delay (td) from the preceding pulse (see Figure 5,

Figure 6, Figure 7, Figure 8 and Figure 9):

• td =t1 (0.7 ms); increments the instruction counter

• td =t2 (1.7 ms); clocks the shift register with data = logic 0

• td =t3 (2.7 ms); clocks the shift register with data = logic 1

The programming procedure requires a stable oscillator, which means that a waiting time,

determined by the start-up time of the oscillator, is necessary after power-up of the circuit.

td(start): start delay time.

VDD(nom): nominal supply voltage.

Fig 4.

Supply voltage at start-up during production and testing

VDD

VP(prog)(stop)

td(start) > 500 ms

VSS

VDD(nom)

001aac503

tp(stop)

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