P89LPC9401 datasheet(17/59 Pages) PHILIPS

17 / 59 page

P89LPC9401_1

Preliminary data sheet

Rev. 01 — 5 September 2005

17 of 59

Philips Semiconductors

P89LPC9401

8-bit two-clock 80C51 microcontroller with 32 segment

× 4 LCD driver

7.3.6 Clock output

The P89LPC9401 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 RTC is not using the crystal oscillator as its clock

source. This allows external devices to synchronize to the P89LPC9401. This output is

enabled by the ENCLK bit in the TRIM register.

The frequency of this clock output is 1

⁄

2 that of the CCLK. If the clock output is not needed

in Idle mode, it may be turned off prior to entering idle, saving additional power.

7.4 On-chip RC oscillator option

The P89LPC9401 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 preprogrammed 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.

7.5 Watchdog oscillator option

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.

7.6 External clock input option

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 VDD has reached its

speciﬁed level. When system power is removed VDD will fall below 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 VDD falls below the minimum speciﬁed operating voltage.

P89LPC9401 Datasheet(PDF) 17 Page - NXP Semiconductors