8-bit microcontroller with accelerated two-clock 80C51 core
8.7 CCLK wake-up delay
The P89LPC933/934/935/936 has an internal wake-up timer that delays the clock until it
stabilizes depending on the clock source used. If the clock source is any of the three
crystal selections (low, medium and high frequencies) the delay is 992 OSCCLK cycles
plus 60 μs to 100 μs. If the clock source is either the internal RC oscillator, watchdog
oscillator, or external clock, the delay is 224 OSCCLK cycles plus 60 μs to 100 μs.
8.8 CCLK modification: DIVM register
The OSCCLK frequency can be divided down up to 510 times by configuring a dividing
register, DIVM, to generate CCLK. This feature makes it possible to temporarily run the
CPU at a lower rate, reducing power consumption. By dividing the clock, the CPU can
retain the ability to respond to events that would not exit Idle mode by executing its normal
program at a lower rate. This can also allow bypassing the oscillator start-up time in cases
where Power-down mode would otherwise be used. The value of DIVM may be changed
by the program at any time without interrupting code execution.
8.9 Low power select
The P89LPC933/934/935/936 is designed to run at 18 MHz (CCLK) maximum. However,
if CCLK is 8 MHz or slower, the CLKLP SFR bit (AUXR1.7) can be set to logic 1 to lower
the power consumption further. On any reset, CLKLP is logic 0 allowing highest
performance access. This bit can then be set in software if CCLK is running at 8 MHz or
8.10 Memory organization
The various P89LPC933/934/935/936 memory spaces are as follows:
128 bytes of internal data memory space (00H:7FH) accessed via direct or indirect
addressing, using instructions other than MOVX and MOVC. All or part of the Stack
may be in this area.
Indirect Data. 256 bytes of internal data memory space (00H:FFH) accessed via
indirect addressing using instructions other than MOVX and MOVC. All or part of the
Stack may be in this area. This area includes the DATA area and the 128 bytes
immediately above it.
Selected CPU registers and peripheral control and status registers, accessible only
via direct addressing.
• XDATA (P89LPC935/936)
‘External’ Data or Auxiliary RAM. Duplicates the classic 80C51 64 kB memory space
addressed via the MOVX instruction using the SPTR, R0, or R1. All or part of this
space could be implemented on-chip. The P89LPC935/936 has 512 bytes of on-chip
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.
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