Philips 8-bit microcontroller with two-clock 80C51 core UM10109 User Manual

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

High frequency crystal

High frequency crystal
/DIVM

High frequency crystal

Internal RC oscillator

001

Medium frequency crystal

Medium frequency crystal
/DIVM

Medium frequency crystal

Internal RC oscillator