P89LPC901FD datasheet(24/55 Pages) PHILIPS

24 / 55 page

Philips Semiconductors

P89LPC901/902/903

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 04 — 21 November 2003

24 of 55

9397 750 12293

Functional description

Remark: Please refer to the

P89LPC901/902/903 User’s Manual for a more detailed

functional description.

8.1 Enhanced CPU

The P89LPC901/902/903 uses an enhanced 80C51 CPU which runs at 6 times the

speed of standard 80C51 devices. A machine cycle consists of two CPU clock cycles,

and most instructions execute in one or two machine cycles.

8.2 Clocks

8.2.1

Clock deﬁnitions

The P89LPC901/902/903 device has several internal clocks as deﬁned below:

OSCCLK — Input to the DIVM clock divider. OSCCLK is selected from one of the

clock sources (see Figures 12, 13, and 14) and can also be optionally divided to a

slower frequency (see Section 8.7 “CPU CLOCK (CCLK) modiﬁcation: DIVM

Note: fOSC is deﬁned as the OSCCLK frequency.

CCLK — CPU clock; output of the clock divider. There are two CCLK cycles per

machine cycle, and most instructions are executed in one to two machine cycles (two

or four CCLK cycles).

RCCLK — The internal 7.373 MHz RC oscillator output.

PCLK — Clock for the various peripheral devices and is CCLK/2

8.2.2

CPU clock (OSCCLK)

The P89LPC901/902/903 provides several user-selectable oscillator options in

generating the CPU clock. This allows optimization for a range of needs from high

precision to lowest possible cost. These options are conﬁgured when the FLASH is

programmed and include an on-chip Watchdog oscillator and an on-chip RC

oscillator.

The P89LPC901, in addition, includes an option for an oscillator using an external

crystal or an external clock source. The crystal oscillator can be optimized for low,

medium, or high frequency crystals covering a range from 20 kHz to 12 MHz.

8.2.3

Low speed oscillator option (P89LPC901)

This option supports an external crystal in the range of 20 kHz to 100 kHz. Ceramic

resonators are also supported in this conﬁguration.

8.2.4

Medium speed oscillator option (P89LPC901)

This option supports an external crystal in the range of 100 kHz to 4 MHz. Ceramic

resonators are also supported in this conﬁguration.

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