pca2125 NXP Semiconductors, pca2125 Datasheet - Page 17

• Manufacturer Part Number: pca2125
• Description: Spi Real Time Clock / Calendar Semiconductors
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA2125_00
Preliminary data sheet
6.6.2 Countdown timer function
The 8-bit countdown timer at address 0F
address 0E
for the timer (4096 Hz, 64 Hz, 1 Hz, or
Table 30.
[1]
Remark: Note that all timings which are generated from the 32.768kHz oscillator are
based on the assumption that there is 0 ppm deviation. Deviation in oscillator frequency
will result in 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 (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
If a new value of n is written before the end of the current timer period, then this value will
take immediate effect. NXP does not recommend to changing n without first disabling the
counter (by setting TE = 0). The update of n is asynchronous to the timer clock, therefore
changing it without setting TE = 0 will result in a corrupted value loaded into the
CDT1
0
0
1
1
Fig 11. General countdown timer behavior
countdown value, n
countdown counter
timer source clock
When not in use, CDT must be set to
In the example it is assumed that the timer flag is cleared before the next countdown period
expires and that the INT is set to pulsed mode.
CDT1 and CDTD: Timer frequency selection
HEX
CDT0
0
1
0
1
INT
TE
TF
. The timer control register determines one of 4 source clock frequencies
xx
xx
Rev. 00.11 — 30 January 2007
TIMER Source clock frequency
4096 Hz
64 Hz
1 Hz
1⁄60 Hz
03
03
Figure
1
⁄
11)..
60
Hz for power saving.
1
⁄
60
HEX
02
Hz), and enables or disables the timer.
is controlled by the timer control register at
duration of first timer period after
enable may range from n − 1 to n + 1
01
03
SPI Real time clock / calendar
02
n
[1]
01
delay for
n = 1
244 µs
15.625 ms
1 s
60 s
03
PCA2125
© NXP B.V. 2007. All rights reserved.
02
n
delay for
n = 255
62.256 ms
3.984 s
255 s
4 hrs 15 min
01
001aaf906
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03