PCA88021 datasheet(16/34 Pages) NXP

16 / 34 page

PCA8802_1

Product data sheet

Rev. 01 — 19 February 2009

16 of 34

NXP Semiconductors

PCA8802

Smartcard RTC

9.6.5 Instruction 32k_cmd

The 32.768 kHz enable instruction (32k_cmd) is intended to aid with oscillator

characterization during system development. With this instruction it is possible to obtain a

32.768 kHz clock on the INT pin which may be used for measurement.

This mode does not affect other operation of the chip with the exception of loss of interrupt

output.

9.6.6 Instruction fst_cmd

The fast mode instruction (fst_cmd) is intended to enable faster system development.

When enabled, the counter will increment once every second instead of once every 32

seconds. Interrupt pulses will also be generated once every second.

When using fst_cmd, data access to the device must be completed within 1 second, if not

then counter increments will be lost. The 1 second period is measured from the ACK cycle

of a valid slave address to the next STOP or repeated START. A repeated START will be

sufﬁcient to allow the counter to increment.

9.6.7 Instruction set_cmd

The counter can be set to any value using the set instruction (set_cmd). Partial writing of

the data parameters will result in partial setting of the counter. E.g. if data transfer is

stopped after P1[23:16] is transmitted, then only bit 23 to bit 16 will be updated.

Table 7.

Power-down sequence

Step Action

Code sequence Note

To enter power-down

initiate transfer

START condition -

send wrt_cmd

1010 0000

enable dvs_cmd

0001 0001

stop the divider

set counter with set_cmd

1000 0000

set the counter = AAAAAAh

1010 1010

P1[23:16]

1010 1010

P2[15:8]

1010 1010

P3[7:0]

enable pwd_cmd

0010 0001

stop the oscillator

end transfer

STOP condition

device is now in a

power-down state

To exit power-down

initiate transfer

START condition -

send wrt_cmd

1010 0000

disable pwd_cmd

0010 0000

oscillator starts on the ACK cycle of this

instruction

disable dvs_cmd

0001 0000

enable the divider again

end transfer

STOP condition

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