pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 38

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCF2127A_1
Product data sheet
8.11.4 Countdown timer function
The countdown timer function is controlled by the WD_CD[1:0] bits in register
Watchdg_tim_ctl (see
The timer counts down from the software programmed 8 bit binary value n in register
Watchdg_tim_val. When the counter reaches 1
Loading the counter with 0 effectively stops the timer.
Reading the timer will return the actual value of the countdown counter.
Fig 22. WD_CD[1:0] = 11: watchdog activates a reset pulse when timed out
Fig 23. General countdown timer behavior
•
•
•
countdown value, n
timer value
countdown counter
the countdown timer flag CDTF is set
the counter automatically reloads
and the next time period starts
timer source clock
watchdog
WDTF
WD/CD [1:0]
RST
Counter reached 1, WDTF is set logic 1, reset pulse on the RST pin is generated for a time equal
to t
In this example it is assumed that the countdown timer flag (CDTF) is cleared before the next
countdown period expires and that INT is set to pulsed mode.
w(rst)
CDTF
INT
.
XX
XX
00
Rev. 01 — 21 January 2010
Table
03
03
n = 1
34).
t
w(rst)
01
02
duration of first timer period after
enable may range from n−1 to n+1
Integrated RTC, TCXO and quartz crystal
01
03
02
n
01
PCF2127A
03
© NXP B.V. 2010. All rights reserved.
02
n
MCU
001aag063
n
001aaf071
01
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03