PCA2125TS NXP [NXP Semiconductors], PCA2125TS Datasheet - Page 15

• Manufacturer Part Number: PCA2125TS
• Description: SPI Real-time clock/calendar
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCA2125_1
Product data sheet
8.6.2 Countdown timer function
Table 27.
[1]
The 8-bit countdown timer at address 0Fh is controlled by the timer control register at
address 0Eh. The timer control register determines one of 4 source clock frequencies for
the timer (4096 Hz, 64 Hz, 1 Hz, or
Table 28.
[1]
Remark: Note that all timings which are generated from the 32.768 kHz oscillator are
based on the assumption that there is 0 ppm deviation. Deviation in oscillator frequency
will result in a corresponding deviation in timings. This is not applicable to interface timing.
The timer counts down from a software-loaded 8-bit binary value n. Loading the counter
with 0 effectively stops the timer. Values from 1 to 255 are valid. When the counter
reaches 1, the countdown timer flag (bit TF) will be set and the counter automatically
re-loads and starts the next timer period. Reading the timer will return the current value of
the countdown counter; see
Minute interrupt (bit MI)
0
1
0
1
Bits CTD[1:0]
00
01
10
11
In the case of bit MI = 1 and bit SI = 0, bit MSF will be cleared automatically after 1 second.
When not in use, bits CTD[1:0] must be set to
Effect of bits MI and SI on bit MSF
Bits CTD1 and CTD0 for timer frequency selection and countdown timer
durations
Timer source clock
frequency
4096 Hz
64 Hz
1 Hz
1
60
Hz
Rev. 01 — 28 July 2008
Second interrupt (bit SI) Result
0
0
1
1
Figure
10.
1
60
Delay
Minimum timer duration
n = 1
244 s
15.625 ms
1 s
60 s
Hz), and enables or disables the timer.
1
60
[1]
Hz for power saving.
MSF never set
MSF set when minutes counter
increments
MSF set when seconds counter
increments
MSF set when seconds counter
increments
SPI Real-time clock/calendar
[1]
Maximum timer duration
n = 255
62.256 ms
3.984 s
255 s
4 h 15 min
PCA2125
© NXP B.V. 2008. All rights reserved.
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