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© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual Rev. 02 — 23 May 2005 44 of 133
Philips Semiconductors
UM10109
P89LPC932A1 User manual
8.1 Real-time clock source
RTCS1/RTCS0 (RTCCON[6:5]) are used to select the clock source for the RTC if either
the Internal RC oscillator or the internal WD oscillator is used as the CPU clock. If the
internal crystal oscillator or the external clock input on XTAL1 is used as the CPU clock,
then the RTC will use CCLK as its clock source.
8.2 Changing RTCS1/RTCS0
RTCS1/RTCS0 cannot be changed if the RTC is currently enabled (RTCCON.0 = 1).
Setting RTCEN and updating RTCS1/RTCS0 may be done in a single write to RTCCON.
However, if RTCEN = 1, this bit must first be cleared before updating RTCS1/RTCS0.
8.3 Real-time clock interrupt/wake-up
If ERTC (RTCCON.1), EWDRT (IEN1.0.6) and EA (IEN0.7) are set to logic 1, RTCF can
be used as an interrupt source. This interrupt vector is shared with the watchdog timer. It
can also be a source to wake-up the device.
8.4 Reset sources affecting the Real-time clock
Only power-on reset will reset the Real-time Clock and its associated SFRs to their default
state.
Table 25: Real-time Clock/System Timer clock sources
FOSC2:0 RCCLK RTCS1:0 RTC clock source CPU clock source
000 0 00 High frequency crystal High frequency crystal
/DIVM
01
10
11 High frequency crystal
/DIVM
1 00 High frequency crystal Internal RC oscillator
01
10
11 Internal RC oscillator
001 0 00 Medium frequency crystal Medium frequency crystal
/DIVM
01
10
11 Medium frequency crystal
/DIVM
1 00 Medium frequency crystal Internal RC oscillator
01
10
11 Internal RC oscillator