DS87C520 datasheet(18/45 Pages) DALLAS

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DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers

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Table 6. PMM Control and Status Bit Summary

BIT

LOCATION

FUNCTION

RESET

WRITE ACCESS

XT/

EXIF.3

Control. XT/

RG = 1, runs from crystal or external

clock; XT/

RG = 0, runs from internal ring oscillator.

0 to 1 only when

XTUP = 1 and

XTOFF = 0

RGMD

EXIF.2

Status. RGMD = 1, CPU clock = ring; RGMD = 0,

CPU clock = crystal.

None

CD1, CD0

PMR.7,

PMR.6

Control. CD1, 0 = 01, 4 clocks; CS1, 0 = 10, PMM1;

CD1, 0 = 11, PMM2.

0, 1

Write CD1, 0 = 10

or 11 only from

CD1, 0 = 01

SWB

PMR.5

Control. SWB = 1, hardware invokes switchback to 4

clocks, SWB = 0, no hardware switchback.

Unrestricted

XTOFF

PMR.3

Control. Disables crystal operation after ring is

selected.

1 only when

XT/

RG = 0

PIP

STATUS.7

Status. 1 indicates a power-fail interrupt in service.

None

HIP

STATUS.6

Status. 1 indicates high priority interrupt in service.

None

LIP

STATUS.5

Status. 1 indicates low priority interrupt in service.

None

XTUP

STATUS.4

Status. 1 indicates that the crystal has stabilized.

None

SPTA1

STATUS.3

Status. Serial transmission on serial port 1.

None

SPRA1

STATUS.2

Status. Serial word reception on serial port 1.

None

SPTA0

STATUS.1

Status. Serial transmission on serial port 0.

None

SPRA0

STATUS.0

Status. Serial word reception on serial port 0.

None

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