P89LPC924 Philips Semiconductors, P89LPC924 Datasheet - Page 15

• Manufacturer Part Number: P89LPC924
• Description: (P89LPC924 / P89LPC925) 8-bit microcontrollers
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 14471
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 minimum specified operating voltage. When using an oscillator frequency
above 12 MHz, in some applications, an external brownout detect circuit may
be required to hold the device in reset when V
specified operating voltage.
The P89LPC924/925 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
P89LPC924/925. 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 P89LPC924/925 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 18 MHz. The XTAL2/P3.0 pin
may be used as a standard port pin or a clock output. When using an oscillator
frequency above 12 MHz, the reset input function of P1.5 must be enabled. An
external circuit is required to hold the device in reset at power-up until V
reached its specified level. When system power is removed V
the minimum specified operating voltage. When using an oscillator frequency
above 12 MHz, in some applications, an external brownout detect circuit may
be required to hold the device in reset when V
specified operating voltage.
Rev. 03 — 15 December 2004
8-bit microcontrollers with accelerated two-clock 80C51 core
1
2
that of the CCLK. If the clock output is not needed
DD
DD
P89LPC924/925
falls below the minimum
falls below the minimum
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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will fall below
DD
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