PCF2127AT/1 NXP [NXP Semiconductors], PCF2127AT/1 Datasheet - Page 38

• Manufacturer Part Number: PCF2127AT/1
• Description: Integrated RTC, TCXO and quartz crystal
• Manufacturer: NXP [NXP Semiconductors]

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.
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n
001aag071
01
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