P89LPC933FDH datasheet(34/75 Pages) PHILIPS

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9397 750 15113

Product data sheet

Rev. 06 — 20 June 2005

34 of 75

Philips Semiconductors

P89LPC933/934/935/936

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

8.17 Timers/counters 0 and 1

The P89LPC933/934/935/936 has two general purpose counter/timers which are upward

compatible with the standard 80C51 Timer 0 and Timer 1. Both can be conﬁgured to

operate either as timers or event counter. An option to automatically toggle the T0 and/or

T1 pins upon timer overﬂow has been added.

In the ‘timer’ function, the register is incremented every machine cycle.

In the ‘counter’ function, the register is incremented in response to a 1-to-0 transition at its

corresponding external input pin, T0 or T1. In this function, the external input is sampled

once during every machine cycle.

Timer 0 and Timer 1 have ﬁve operating modes (modes 0, 1, 2, 3 and 6). Modes 0, 1, 2

and 6 are the same for both timers/counters. 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

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.

8.17.5 Mode 6

In this mode, the corresponding timer can be changed to a PWM with a full period of

256 timer clocks.

8.17.6 Timer overﬂow toggle output

Timers 0 and 1 can be conﬁgured to automatically toggle a port output whenever a timer

overﬂow occurs. The same device pins that are used for the T0 and T1 count inputs are

also used for the timer toggle outputs. The port outputs will be a logic 1 prior to the ﬁrst

timer overﬂow when this mode is turned on.

8.18 RTC/system timer

The P89LPC933/934/935/936 has a simple RTC that allows a user to continue running an

accurate timer while the rest of the device is powered-down. The RTC can be a wake-up

or an interrupt source. The RTC is a 23-bit down counter comprised of a 7-bit prescaler

and a 16-bit loadable down counter. When it reaches all logic 0s, the counter will be

reloaded again and the RTCF ﬂag will be set. The clock source for this counter can be

either the CPU clock (CCLK) or the XTAL oscillator, provided that the XTAL oscillator is not

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