89LPC925 datasheet(28/49 Pages) PHILIPS

28 / 49 page

Philips Semiconductors

P89LPC924/925

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

Product data

Rev. 03 — 15 December 2004

28 of 49

9397 750 14471

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.

8.17.5

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 Real-Time clock/system timer

The P89LPC924/925 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.

8.19 UART

The P89LPC924/925 has an enhanced UART that is compatible with the

conventional 80C51 UART except that Timer 2 overﬂow cannot be used as a baud

rate source. The P89LPC924/925 does include an independent Baud Rate

Generator. The baud rate can be selected from the oscillator (divided by a constant),

Timer 1 overﬂow, or the independent Baud Rate Generator. In addition to the baud

rate generation, enhancements over the standard 80C51 UART include Framing

Error detection, automatic address recognition, selectable double buffering and

several interrupt options. The UART can be operated in 4 modes: shift register, 8-bit

UART, 9-bit UART, and CPU clock/32 or CPU clock/16.

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