DS87C520 Datasheet, PDF (18/45 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Micro

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers
Table 6. PMM Control and Status Bit Summary
BIT
LOCATION
FUNCTION
XT/RG
EXIF.3
Control. XT/RG = 1, runs from crystal or external
clock; XT/RG = 0, runs from internal ring oscillator.
RGMD
EXIF.2
Status. RGMD = 1, CPU clock = ring; RGMD = 0,
CPU clock = crystal.
CD1, CD0
PMR.7,
PMR.6
Control. CD1, 0 = 01, 4 clocks; CS1, 0 = 10, PMM1;
CD1, 0 = 11, PMM2.
SWB
XTOFF
PIP
HIP
LIP
XTUP
SPTA1
SPRA1
SPTA0
SPRA0
PMR.5
PMR.3
STATUS.7
STATUS.6
STATUS.5
STATUS.4
STATUS.3
STATUS.2
STATUS.1
STATUS.0
Control. SWB = 1, hardware invokes switchback to 4
clocks, SWB = 0, no hardware switchback.
Control. Disables crystal operation after ring is
selected.
Status. 1 indicates a power-fail interrupt in service.
Status. 1 indicates high priority interrupt in service.
Status. 1 indicates low priority interrupt in service.
Status. 1 indicates that the crystal has stabilized.
Status. Serial transmission on serial port 1.
Status. Serial word reception on serial port 1.
Status. Serial transmission on serial port 0.
Status. Serial word reception on serial port 0.
RESET
X
WRITE ACCESS
0 to 1 only when
XTUP = 1 and
XTOFF = 0
0
None
Write CD1, 0 = 10
0, 1 or 11 only from
CD1, 0 = 01
0
Unrestricted
0
1 only when
XT/RG = 0
0
None
0
None
0
None
1
None
0
None
0
None
0
None
0
None
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