P89LPC915FDH datasheet(29/72 Pages) PHILIPS

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Philips Semiconductors

P89LPC915/916/917

8-bit microcontrollers with accelerated two-clock 80C51 core

Product data

Rev. 04 — 17 December 2004

29 of 72

9397 750 14397

Functional description

Remark: Please refer to the

P89LPC915/916/917 User’s Manual for a more detailed

functional description.

9.1 Enhanced CPU

The P89LPC915/916/917 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.

9.2 Clocks

9.2.1

Clock deﬁnitions

The P89LPC915/916/917 device has several internal clocks as deﬁned below:

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

clock sources (see Figure 10) and can also be optionally divided to a slower

frequency (see Section 9.7 “CPU Clock (CCLK) modiﬁcation: DIVM register”).

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

9.2.2

CPU clock (OSCCLK)

The P89LPC915/916/917 provide 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, an on-chip RC oscillator, and an external

clock input.

9.2.3

Clock output (P89LPC917)

The P89LPC917 supports a user selectable clock output function on the CLKOUT

pin. This allows external devices to synchronize to the P89LPC917. This output is

enabled by the ENCLK bit in the TRIM register. The frequency of this clock output is

⁄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.

9.3 On-chip RC oscillator option

The P89LPC915/916/917 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.

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