PCF8523TSSLASH1 datasheet(41/75 Pages) NXP

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PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

41 of 74

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

[1]

n = loaded timer register value. Timer stops when n = 0.

[2]

If pulse period is shorter than the setting via bit TBW[2:0], the interrupt pulse width is set to 15.625 ms.

When flags like SF, CTAF, WTAF, and CTBF are cleared before the end of the interrupt

pulse, then the interrupt pulse is shortened. This allows the source of a system interrupt to

be cleared immediately when it is serviced, that is, the system does not have to wait for

the completion of the pulse before continuing; see Figure 24 and Figure 25. Instructions

for clearing flags can be found in Section 8.7.5. Instructions for clearing the bit WTAF can

be found in Section 8.9.2.1.

Table 44.

Interrupt low pulse width for timer B

Pulse mode, bit TBM set logic 1.

Source clock (Hz).

Interrupt pulse width

n = 1[1]

n > 1[1]

4096

122

s

244

s

7.812 ms

see Table 38[2]

see Table 38

1⁄60

1⁄3600

(1) Indicates normal duration of INT1 pulse.

The timing shown for clearing bit SF is also valid for the non-pulsed interrupt mode, that is, when

TAM set logic 0, where the INT1 pulse may be shortened by setting SIE logic 0.

Fig 24. Example of shortening the INT1 pulse by clearing the SF flag

013aaa333

seconds counter

INT1

SCL

instruction

CLEAR INSTRUCTION

(1)

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