P89LPC904FD datasheet(25/41 Pages) PHILIPS

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Philips Semiconductors

P89LPC904

8-bit microcontrollers with two-clock accelerated 80C51 core

Preliminary data

Rev. 02 — 25 June 2004

25 of 41

9397 750 13521

Reset can be triggered from the following sources:

• External reset pin (during power-up or if user conﬁgured via UCFG1)

• Power-on detect

• Brownout detect

• Watchdog Timer

• Software reset

• UART break character detect reset.

For every reset source, there is a ﬂag in the Reset Register, RSTSRC. The user can

read this register to determine the most recent reset source. These ﬂag bits can be

cleared in software by writing a logic 0 to the corresponding bit. More than one ﬂag bit

may be set:

• During a power-on reset, both POF and BOF are set but the other ﬂag bits are

cleared.

• For any other reset, previously set ﬂag bits that have not been cleared will remain

set.

8.17 Timers/counters 0 and 1

The P89LPC904 has two general purpose timers which are similar to the standard

80C51 Timer 0 and Timer 1. These timers have four operating modes (modes 0, 1, 2,

and 3). Modes 0, 1, and 2 are the same for both Timers. Mode 3 is different.

8.17.1

Mode 0

Putting either Timer into Mode 0 makes it look like an 8048 Timer, which is an 8-bit

Counter with a divide-by-32 prescaler. In this mode, the Timer register is conﬁgured

as a 13-bit register. Mode 0 operation is the same for Timer 0 and Timer 1.

8.17.2

Mode 1

Mode 1 is the same as Mode 0, except that all 16 bits of the timer register are used.

8.17.3

Mode 2

Mode 2 conﬁgures the Timer register as an 8-bit Counter with automatic reload.

Mode 2 operation is the same for Timer 0 and Timer 1.

8.17.4

Mode 3

When Timer 1 is in Mode 3 it is stopped. Timer 0 in Mode 3 forms two separate 8-bit

counters and is provided for applications that require an extra 8-bit timer. When

Timer 1 is in Mode 3 it can still be used by the serial port as a baud rate generator.

8.18 Real-Time clock/system timer

The P89LPC904 has a simple Real-Time clock that allows a user to continue running

an accurate timer while the rest of the device is powered-down. The Real-Time clock

can be a wake-up or an interrupt source. The Real-Time clock is a 23-bit down

counter comprised of a 7-bit prescaler and a 16-bit loadable down counter. When it

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