P89LPC932BA datasheet(27/60 Pages) PHILIPS

27 / 60 page

Philips Semiconductors

P89LPC932

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

Product data

Rev. 04 — 06 January 2004

27 of 60

9397 750 12379

8.17 Real-Time clock/system timer

The P89LPC932 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

reaches all ‘0’s, 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 being used as the CPU clock. If the

XTAL oscillator is used as the CPU clock, then the RTC will use CCLK as its clock

source. Only power-on reset will reset the Real-Time clock and its associated SFRs

to the default state.

8.18 Capture/Compare Unit (CCU)

This unit features:

• A 16-bit timer with 16-bit reload on overﬂow.

• Selectable clock, with prescaler to divide clock source by any integral number

between 1 and 1024.

• 4 Compare/PWM outputs with selectable polarity

• Symmetrical/Asymmetrical PWM selection

• 2 Capture inputs with event counter and digital noise rejection ﬁlter

• 7 interrupts with common interrupt vector (one Overﬂow, 2 Capture, 4 Compare)

• Safe 16-bit read/write via shadow registers.

8.18.1

CCU clock (CCUCLK)

The CCU runs on the CCUCLK, which is either PCLK in basic timer mode, or the

output of a PLL. The PLL is designed to use a clock source between 0.5 MHz to

1 MHz that is multiplied by 32 to produce a CCUCLK between 16 MHz and 32 MHz in

PWM mode (asymmetrical or symmetrical). The PLL contains a 4-bit divider to help

divide PCLK into a frequency between 0.5 MHz and 1 MHz.

8.18.2

CCU clock prescaling

This CCUCLK can further be divided down by a prescaler. The prescaler is

implemented as a 10-bit free-running counter with programmable reload at overﬂow.

8.18.3

Basic timer operation

The Timer is a free-running up/down counter with a direction control bit. If the timer

counting direction is changed while the counter is running, the count sequence will be

reversed. The timer can be written or read at any time.

When a reload occurs, the CCU Timer Overﬂow Interrupt Flag will be set, and an

interrupt generated if enabled. The 16-bit CCU Timer may also be used as an 8-bit

up/down timer.

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