PCA2002_5

© NXP B.V. 2008. All rights reserved.

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.

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

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

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.

Fig 4.

Supply voltage at start-up during production and testing

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