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
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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.
