NXP Semiconductors
P89LPC933/934/935/936
8-bit microcontroller with accelerated two-clock 80C51 core
8.2 Enhanced CPU
The P89LPC933/934/935/936 uses an enhanced 80C51 CPU which runs at six 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.
8.3 Clocks
8.3.1 Clock definitions
The P89LPC933/934/935/936 device has several internal clocks as defined below:
OSCCLK — Input to the DIVM clock divider. OSCCLK is selected from one of four clock
sources (see Figure 8) and can also be optionally divided to a slower frequency (see
Section 8.8 “CCLK modification: DIVM register”).
Remark: 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.
8.3.2 CPU clock (OSCCLK)
The P89LPC933/934/935/936 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, an on-chip RC oscillator, 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
18 MHz.
8.3.3 Low speed oscillator option
This option supports an external crystal in the range of 20 kHz to 100 kHz. Ceramic
resonators are also supported in this configuration.
8.3.4 Medium speed oscillator option
This option supports an external crystal in the range of 100 kHz to 4 MHz. Ceramic
resonators are also supported in this configuration.
8.3.5 High speed oscillator option
This option supports an external crystal in the range of 4 MHz to 18 MHz. Ceramic
resonators are also supported in this configuration.
8.3.6 Clock output
The P89LPC933/934/935/936 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,
P89LPC933_934_935_936
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 8 — 12 January 2011
© NXP B.V. 2011. All rights reserved.
24 of 77