P89LPC920FDH PHILIPS [NXP Semiconductors], P89LPC920FDH Datasheet - Page 15

• Manufacturer Part Number: P89LPC920FDH
• Description: 8-bit microcontrollers with two-clock 80C51 core 2 kB/4 kB/8 kB 3 V low-power Flash with 256-byte data RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 12285
Product data
8.2.6 Clock output
8.3 On-chip RC oscillator option
8.4 Watchdog oscillator option
8.5 External clock input option
The P89LPC920/921/922 supports a user-selectable clock output function on the
XTAL2/CLKOUT pin when crystal oscillator is not being used. This condition occurs if
another clock source has been selected (on-chip RC oscillator, watchdog oscillator,
external clock input on X1) and if the Real-Time clock is not using the crystal
oscillator as its clock source. This allows external devices to synchronize to the
P89LPC920/921/922. This output is enabled by the ENCLK bit in the TRIM register.
The frequency of this clock output is
needed in Idle mode, it may be turned off prior to entering Idle, saving additional
power.
The P89LPC920/921/922 has a 6-bit TRIM register that can be used to tune the
frequency of the RC oscillator. During reset, the TRIM value is initialized to a factory
pre-programmed value to adjust the oscillator frequency to 7.373 MHz, 1% at room
temperature. End-user applications can write to the Trim register to adjust the on-chip
RC oscillator to other frequencies.
The watchdog has a separate oscillator which has a frequency of 400 kHz. This
oscillator can be used to save power when a high clock frequency is not needed.
In this configuration, the processor clock is derived from an external source driving
the XTAL1/P3.1 pin. The rate may be from 0 Hz up to 12 MHz. The XTAL2/P3.0 pin
may be used as a standard port pin or a clock output.
Fig 5. Block diagram of oscillator control.
XTAL1
XTAL2
OSCILLATOR
(7.3728 MHz)
OSCILLATOR
TIMER 0 and
WATCHDOG
Rev. 06 — 21 November 2003
(400 kHz)
TIMER 1
RC
Med. freq.
High freq.
Low freq.
PCLK
I
2
8-bit microcontrollers with two-clock 80C51 core
C
1
OSCCLK
2
that of the CCLK. If the clock output is not
GENERATOR
BAUD RATE
P89LPC920/921/922
DIVM
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
CCLK
UART
2
002aaa424
WDT
CPU
RTC
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