PCF2127TSLASH2Y datasheet(46/100 Pages) PHILIPS

46 / 100 page

PCF2127

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Product data sheet

Rev. 8 — 19 December 2014

46 of 100

NXP Semiconductors

PCF2127

Accurate RTC with integrated quartz crystal for industrial applications

When reading the timer, the actual countdown value is returned and not the initial value n.

Since it is not possible to freeze the countdown timer counter during read back, it is

recommended to read the register twice and check for consistent results.

8.11.5 Pre-defined timers: second and minute interrupt

PCF2127 has two pre-defined timers which are used to generate an interrupt either once

per second or once per minute (see Section 8.13.1). The pulse generator for the minute or

second interrupt operates from an internal 64 Hz clock. It is independent of the watchdog

or countdown timers. Each of these timers can be enabled by the bits SI (second interrupt)

and MI (minute interrupt) in register Control_1.

8.11.6 Clearing flags

The flags MSF, CDTF, AF and TSFx can be cleared by command. To prevent one flag

being overwritten while clearing another, a logic AND is performed during the write

access. A flag is cleared by writing logic 0 while a flag is not cleared by writing logic 1.

Writing logic 1 results in the flag value remaining unchanged.

Four examples are given for clearing the flags. Clearing the flags is made by a write

command:

• Bits labeled with - must be written with their previous values

• WDTF is read only and has to be written with logic 0

Repeatedly rewriting these bits has no influence on the functional behavior.

The following tables show what instruction must be sent to clear the appropriate flag.

[1]

The bits labeled as - have to be rewritten with the previous values.

[1]

The bits labeled as - have to be rewritten with the previous values.

Table 61.

Flag location in register Control_2

Bit

Control_2

MSF

WDTF

TSF2

CDTF

Table 62.

Example values in register Control_2

Bit

Control_2

101

11000

Table 63.

Example to clear only CDTF (bit 3)

Bit

Control_2

-[1]

Table 64.

Example to clear only AF (bit 4)

Bit

Control_2

0[1]

PCF2127T/2Y Datasheet(PDF) 46 Page - NXP Semiconductors

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