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Philips Semiconductors
User’s Manual - Preliminary -
P89LPC901/902/903
REAL-TIME CLOCK/SYSTEM TIMER
2003 Dec 8 53
Table 6-2: :Real-time Clock/System Timer Clock Source - P89LPC902/903
Changing RTCS1-0
RTCS1-0 cannot be changed if the RTC is currently enabled (RTCCON.0 =1). Setting RTCEN and updating RTCS1-0 may be
done in a single write to RTCCON. However, if RTCEN = 1, this bit must first be cleared before updating RTCS1-0
Real-time Clock Interrupt/Wake Up
If ERTC (RTCCON.1), EWDRT (IEN0.6) and EA (IEN0.7) are set to ’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.
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.
FOSC2
(UCFG1.2)
FOSC1
(UCFG1.1)
FOSC0
(UCFG1.0)
RTCS1:0
CCLK Frequency RTC Clock Frequency
000
x undefined001
010
011
00
RC Oscillator/DIVM
undefined01
10
11 RC Oscillator/DIVM (CCLK)
100
00
WDT Oscillator/DIVM
undefined01
10
11
WDT Oscillator/DIVM
(CCLK)
101
xx undefined110
111