P89LPC915FDH NXP [NXP Semiconductors], P89LPC915FDH Datasheet - Page 29

• Manufacturer Part Number: P89LPC915FDH
• Description: 8-bit microcontrollers with accelerated two-clock 80C51 core 2 kB 3 V flash with 8-bit A/D converter
• Manufacturer: NXP [NXP Semiconductors]

Philips Semiconductors
9. Functional description
9397 750 14397
Product data
9.2.1 Clock definitions
9.2.2 CPU clock (OSCCLK)
9.2.3 Clock output (P89LPC917)
9.1 Enhanced CPU
9.2 Clocks
9.3 On-chip RC oscillator option
Remark: Please refer to the P89LPC915/916/917 User’s Manual for a more detailed
functional description.
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.
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
frequency (see
Note: f
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
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.
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
1
off prior to entering Idle, saving additional power.
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.
2
that of the CCLK. If the clock output is not needed in Idle mode, it may be turned
osc
is defined as the OSCCLK frequency.
Section 9.7 “CPU Clock (CCLK) modification: DIVM
Rev. 04 — 17 December 2004
Figure
8-bit microcontrollers with accelerated two-clock 80C51 core
10) and can also be optionally divided to a slower
P89LPC915/916/917
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
register”).
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