Datasheet

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/RG
EXIF.3
Control. XT/RG = 1, runs from crystal or external
clock; XT/RG = 0, runs from internal ring oscillator.
X
0 to 1 only when
XTUP = 1 and
XTOFF = 0
RGMD EXIF.2
Status. RGMD = 1, CPU clock = ring; RGMD = 0,
CPU clock = crystal.
0 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.
0 Unrestricted
XTOFF PMR.3
Control. Disables crystal operation after ring is
selected.
0
1 only when
XT/RG = 0
PIP STATUS.7
Status. 1 indicates a power-fail interrupt in service
.
0 None
HIP STATUS.6 Status. 1 indicates high priority interrupt in service. 0 None
LIP STATUS.5 Status. 1 indicates low priority interrupt in service. 0 None
XTUP STATUS.4 Status. 1 indicates that the crystal has stabilized. 1 None
SPTA1 STATUS.3 Status. Serial transmission on serial port 1. 0 None
SPRA1 STATUS.2 Status. Serial word reception on serial port 1. 0 None
SPTA0 STATUS.1 Status. Serial transmission on serial port 0. 0 None
SPRA0 STATUS.0 Status. Serial word reception on serial port 0. 0 None