PCF2127AT/1,518 NXP Semiconductors, PCF2127AT/1,518 Datasheet - Page 38

• Manufacturer Part Number: PCF2127AT/1,518
• Description: IC RTC/CALENDAR TCXO QTZ 20SOIC
• Manufacturer: NXP Semiconductors
• Type: Clock/Calendar/Alarmr

Specifications of PCF2127AT/1,518

• Package / Case: 20-SOIC (0.300", 7.50mm Width)
• Time Format: HH:MM:SS (12/24 hr)
• Memory Size: 512B
• Date Format: YY-MM-DD-dd
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 1.8 V ~ 4.2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Function: Serial Clock, Timestamp, Timekeeper, Watchdog, Alarm, Calendar, Timer, Timer Interrupt
• Rtc Memory Size: 512 bytes
• Supply Voltage (max): 4.2 V
• Supply Voltage (min): 1.8 V
• Mounting Style: SMD/SMT
• Rtc Bus Interface: I2C
• Supply Current: 2600 nA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

NXP Semiconductors
PCF2127A_2
Product data sheet
8.11.4 Countdown timer function
Table 37.
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.
If a new value of n is written before the end of the actual timer period, this value will take
immediate effect. It is not recommended to change n without first disabling the counter by
setting WD_CD[1:0] = 00. The update of n is asynchronous to the timer clock. Therefore
changing it on the fly could result in a corrupted value loaded into the countdown counter.
This can result in an undetermined countdown period for the first period. The countdown
value n will, however, be correctly stored and correctly loaded on subsequent timer
periods.
WD_CD[1:0]
11
Fig 23. General countdown timer behavior
•
•
•
countdown value, n
countdown counter
the countdown timer flag CDTF is set
the counter automatically reloads
and the next time period starts
timer source clock
WD/CD [1:0]
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.
Specification of t
CDTF
INT
All information provided in this document is subject to legal disclaimers.
XX
XX
00
Table
TF[1:0]
00
01
10
11
03
03
Rev. 02 — 7 May 2010
w(rst)
34).
01
t
244 μs
15.625 ms
15.625 ms
15.625 ms
w(rst)
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
001aag071
01
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03