PCA2002 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 8 — 25 November 2011 8 of 30
NXP Semiconductors
PCA2002
32 kHz watch circuit with programmable output period and pulse width
8.6 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 V
P(prog)(start)
. After this large pulse, an
initial waiting time of t
0
is required. The programming instructions are then entered by
modulating the supply voltage with small pulses (amplitude V
P(mod)
and pulse width t
mod
).
The first small pulse defines the start time, the following pulses perform three different
functions, depending on the time delay (t
d
) from the preceding pulse (see Figure 5,
Figure 6
, Figure 7, Figure 8 and Figure 9):
• t
d
=t
1
(0.7 ms); increments the instruction counter
• t
d
=t
2
(1.7 ms); clocks the shift register with data = logic 0
• t
d
=t
3
(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.
t
d(start)
: start delay time.
V
DD(nom)
: nominal supply voltage.
Fig 4. Supply voltage at start-up during production and testing
V
DD
V
P(prog)(stop)
t
d(start)
> 500 ms
V
SS
V
DD(nom)
001aac503
t
p(stop)
