PCF2123_09 Datasheet, PDF (20/55 Pages) NXP Semiconductors – SPI Real time clock/calendar

NXP Semiconductors
PCF2123
SPI Real time clock/calendar
9.8.2 Register Countdown_timer
Table 25. Register Countdown_timer (address 0Ah) bits description
Bit Symbol
Value
Description
7 to 0 COUNTDOWN_TIMER[7:0] 0h to FFh countdown period in seconds:
CountdownPeriod = _S----_o---_u----_r--_c---_e---_C-----_l--_o---_c-ⁿ--_k---_F----_r---_e---_q---_u---_e---_n----_c---_y-
where n is the countdown value
Reference
Section 9.8.4
9.8.3 Minute and second interrupt
The minute and second interrupts (bits MI and SI) are pre-defined timers for generating
periodic interrupts. The timers can be enabled independently from one another. However,
a minute interrupt enabled on top of a second interrupt will not be distinguishable since it
will occur at the same time; see Figure 15.
seconds counter 58 59
59 00
00 01
minutes counter
11 12
INT when SI enabled
MSF when SI enabled
INT when only MI enabled
MSF when only MI enabled
001aaf905
In this example, TI_TP is set to logic 1 resulting in ¹â„₆₄ Hz wide interrupt pulse and the MSF flag is
not cleared after an interrupt.
Fig 15. INT example for MI and SI
Table 26. Effect of bits MI and SI on INT generation
Minute interrupt (bit MI) Second interrupt (bit SI) Result
0
0
no interrupt generated
1
0
an interrupt once per minute
0
1
an interrupt once per second
1
1
an interrupt once per second
The minute and second flag (bit MSF) is set logic 1 when either the seconds or the
minutes counter increments according to the currently enabled interrupt. The flag can be
read and cleared by the interface. The status of bit MSF does not affect the INT pulse
generation. If the MSF flag is not cleared prior to the next coming interrupt period, an INT
pulse will still be generated.
The purpose of the flag is to allow the controlling system to interrogate the PCF2123 and
identify the source of the interrupt, i.e., minute or second, countdown timer or alarm.
PCF2123_2
Product data sheet
Rev. 02 — 4 December 2009
© NXP B.V. 2009. All rights reserved.
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