PCF2129AT NXP [NXP Semiconductors], PCF2129AT Datasheet - Page 31

• Manufacturer Part Number: PCF2129AT
• Description: Integrated RTC, TCXO and quartz crystal
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCF2129A_1
Product data sheet
8.10.4 Pre-defined timers: second and minute interrupt
8.10.5 Clearing flags
The watchdog timer flag WDTF is read only and cannot be cleared with the interface.
WDTF can be cleared by
Writing logic 0 or logic 1 to WDTF has no effect.
PCF2129A has two pre-defined timers which are used to generate an interrupt either once
per second or once per minute. The pulse generator for the minute or second interrupt
operates from an internal 64 Hz clock. It is independent of the watchdog timer. Each of
these timers can be enabled by the bits SI (second interrupt) and MI (minute interrupt) in
register Control_1.
The flags MSF, AF, and TSFx can be cleared by using the interface. 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 whilst a flag is not cleared by writing logic 1.
Writing logic 1 will result in the flag value remaining unchanged.
Two examples are given for clearing the flags. Clearing a flag is made by a write
command:
Repeatedly re-writing these bits has no influence on the functional behavior.
Fig 17. WD_CD set logic 1: watchdog activates an interrupt when timed out
•
•
•
•
•
•
•
timer value
When the watchdog timer counter reaches 1, the watchdog timer flag WDTF (register
Control_2) is set logic 1
When a minute or second interrupt occurs, the minute/second flag MSF (register
Control_2) is set logic 1 (see
loading a value in register Watchdg_tim_val
reading of the register Control_2
Bits labeled with - must be written with their previous values
Bits labeled with T have to be written with logic 0
WDTF is read only and has to be written with logic 0
watchdog
WDTF
INT
Counter reached 1, WDTF is logic 1, an interrupt is generated.
Rev. 01 — 13 January 2010
n = 1
Section
8.12.1).
Integrated RTC, TCXO and quartz crystal
PCF2129A
© NXP B.V. 2010. All rights reserved.
MCU
n
001aag062
31 of 68