Datasheet

PCF8523 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 17 September 2013 20 of 78
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
8.6.1 Register Seconds
[1] Start-up value.
8.6.1.1 Oscillator STOP flag
The OS flag is set whenever the oscillator is stopped (see Figure 12
). The flag remains
set until cleared by using the interface. When the oscillator is not running, then the OS flag
cannot be cleared. This method can be used to monitor the oscillator.
The oscillator may be stopped, for example, by grounding one of the oscillator pins, OSCI
or OSCO. The oscillator is also considered to be stopped during the time between
power-on and stable crystal resonance. This time may be in a range of 200 ms to 2 s,
depending on crystal type, temperature, and supply voltage. At power-on, the OS flag is
always set.
Table 12. Seconds - seconds and clock integrity status register (address 03h) bit
description
Bit Symbol Value Place value Description
7 OS 0 - clock integrity is guaranteed
1
[1]
- clock integrity is not guaranteed;
oscillator has stopped or been
interrupted
6 to 4 SECONDS 0 to 5 ten’s place actual seconds coded in BCD
format
3 to 0 0 to 9 unit place
Table 13. SECONDS coded in BCD format
Seconds value in
decimal
Upper-digit (ten’s place) Digit (unit place)
Bit Bit
6 5 4 3 2 1 0
00 0000000
01 0000001
02 0000010
: :::::::
09 0001001
10 0010000
: :::::::
58 1011000
59 1011001