ST ST10F276E - RTCDH & RTCDL: RTC Divider Counters; Figure 190. Prescaler Register

Real time clock UM0404
468/564 DocID13284 Rev 2
RTCPH (ED08h) XBUS Reset Value: - - - xh
Figure 190. Prescaler register
The value stored into RTCPH, RTCPL is called RTCP (coded on 20-bit). The dividing ratio
of the Prescaler divider is:
ratio = 64 x (RTCP)
The minimum value which can be set in RTCPL is 0002h.
22.1.3 RTCDH & RTCDL: RTC divider counters
Every basic reference clock the Divider counters are reloaded with the value stored RTCPH
and RTCPL registers. To get an accurate time measurement it is possible to read the value
of the Divider, reading the RTCDH, RTCDL. Those counters are read only. After any bit
changed in the programmable Prescaler register, the new value is loaded in the Divider.
RTCDL (ED0Ah) XBUS Reset Value: xxxxh
RTCDH (ED0Ch) XBUS Reset Value: - - - xh
Note: These registers are not reset, and are read only.
The divider works as a decrementor: when the internal value reaches 0001h, the second
interrupt is generated. Then, when next decrement occurs (which would virtually put in the
divider register the value 0000h), the 20-bit word stored into RTCPH, RTCPL registers is
loaded in the divider. As already stated, the minimum value which can be programmed in
RTCPL is 0002h: if 0001h were set, just one second interrupt would be generated, since the
divider would stay fixed at the value 0001h forever (successive second interrupt cannot
occur).
1514131211109876543210
------------ RTCPH
RW
3 2 1 07 6 5 411 10 9 815 14 13 123 2 1 0
RTCPH
RTCPL
3 2 1 07 6 5 411 10 9 815 14 13 1219 18 17 16
20 bit word counter
1514131211109876543210
RTCDL
R
1514131211109876543210
------------ RTCDH
R