P89LPC938FDH datasheet(21/68 Pages) PHILIPS

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9397 750 14051

Product data sheet

Rev. 01 — 25 February 2005

21 of 68

Philips Semiconductors

P89LPC938

8-bit microcontroller with 10-bit A/D converter

7.7 CCLK wake-up delay

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

µs. If the clock source is either the internal RC oscillator, watchdog oscillator, or

external clock, the delay is 224 OSCCLK cycles plus 60

µsto100 µs.

7.8 CCLK modiﬁcation: DIVM register

The OSCCLK frequency can be divided down up to 510 times by conﬁguring a dividing

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.

7.9 Low power select

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.

7.10 Memory organization

The various P89LPC938 memory spaces are as follows:

• 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.

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