P89LPC938 NXP Semiconductors, P89LPC938 Datasheet - Page 21

• Manufacturer Part Number: P89LPC938
• Description: The P89LPC938 is a single-chip microcontroller, available in low cost packages, based ona high performance processor architecture that executes instructions in two to four clocks,six times the rate of standard 80C51 devices
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14051
Product data sheet
7.10 Memory organization
7.7 CCLK wake-up delay
7.8 CCLK modification: DIVM register
7.9 Low power select
The P89LPC938 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 to 100 s. If the clock source is either the internal RC oscillator, watchdog oscillator, or
external clock, the delay is 224 OSCCLK cycles plus 60 s to 100 s.
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.
The P89LPC938 is designed to run at 12 MHz (CCLK) maximum. However, if CCLK is
8 MHz or slower, the CLKLP SFR bit (AUXR1.7) can be set to ‘1’ to lower the power
consumption further. On any reset, CLKLP is ‘0’ allowing highest performance access.
This bit can then be set in software if CCLK is running at 8 MHz or slower.
The various P89LPC938 memory spaces are as follows:
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DATA
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.
IDATA
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.
SFR
Special Function Registers. Selected CPU registers and peripheral control and status
registers, accessible only via direct addressing.
XDATA
‘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 P89LPC938 has 512 bytes of on-chip
XDATA memory, plus extended SFRs located in XDATA.
Rev. 01 — 25 February 2005
8-bit microcontroller with 10-bit A/D converter
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
P89LPC938
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