P89LPC901 PHILIPS [NXP Semiconductors], P89LPC901 Datasheet - Page 25

• Manufacturer Part Number: P89LPC901
• Description: 8-bit microcontrollers with two-clock 80C51 core 1 kB 3 V Flash with 128-byte RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 12293
Product data
8.2.5 High speed oscillator option (P89LPC901)
8.2.6 Clock output (P89LPC901)
8.3 On-chip RC oscillator option
8.4 Watchdog oscillator option
8.5 External clock input option (P89LPC901)
This option supports an external crystal in the range of 4 MHz to 12 MHz. Ceramic
resonators are also supported in this configuration. If CCLK is 8 MHz or slower, the
CLKLP SFR bit (AUXR1.7) can be set to ‘1’ to reduce power consumption. On reset,
CLKLP is ‘0’ allowing highest performance access. This bit can then be set in
software if CCLK is running at 8 MHz or slower.
The P89LPC901 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
P89LPC901. This output is enabled by the ENCLK bit in the TRIM register. The
frequency of this clock output is
in Idle mode, it may be turned off prior to entering Idle, saving additional power.
The P89LPC901/902/903 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, 2.5%.
End-user applications can write to the Trim register to adjust the on-chip RC oscillator
to other frequencies. If CCLK is 8 MHz or slower, the CLKLP SFR bit (AUXR1.7) can
be set to ‘1’ to reduce power consumption. On reset, CLKLP is ‘0’ allowing highest
performance access. This bit can then be set in software if CCLK is running at 8 MHz
or slower.
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.
Rev. 04 — 21 November 2003
1
8-bit microcontrollers with two-clock 80C51 core
2
that of the CCLK. If the clock output is not needed
P89LPC901/902/903
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
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