MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 101

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

3.8.2 System Status Bits
The eight most significant bits of the SCR are used to report events recognized by the sys-
tem control logic. On recognition of an event, this logic sets the corresponding bit in the
SCR. The bits may be read at any time. A bit is reset by one and is left unchanged by zero.
More than one bit may be reset at a time.
After system reset (simultaneous assertion of RESET and HALT), these bits are cleared.
IPA—Interrupt Priority Active
MOTOROLA
This bit is set when the M68000 core has an unmasked interrupt request. When bus clear
mask (BCLM) is set, BCLR and the internal bus clear to the IDMA are asserted.
If BCLM is set, an interrupt handler will normally clear IPA at the
end of the interrupt routine to allow an alternate bus master to
regain the bus; however, if BCLM is cleared, no additional action
need be taken in the interrupt handler.
In the case of nested interrupts, the user may wish to clear the
IPA bit only at the end of the original lower priority interrupt rou-
tine to keep BCLR asserted until it completes. To guarantee that
HWDEN
HWDCN
RMCST
LPREC
EMWS
WPVE
LPP16
FRZW
ERRE
ADCE
BCLM
LPCD
LPEN
FRZ1
FRZ2
HWT
WPV
SAM
ADC
VGE
IPA
Bit
Interrupt Priority Active
Hardware Watchdog Timeout
Write Protect Violation
Address Decode Conflict
External RISC Request Enable
Vector Generation Enable
Write Protect Violation Enable
Read-Modify-Write Cycle Special Treatment
External Master Wait State
Address Decode Conflict Enable
Bus Clear Mask
Freeze Watchdog Timer Enable
Freeze Timer 1 Enable
Freeze Timer 2 Enable
Synchronous Access Mode
Hardware Watchdog Enable
Hardware Watchdog Count
Low-Power Recovery
Low-Power Clock Prescale Divide by 16
Low-Power Enable
Low-Power Clock Divider Selects
Table 3-9. SCR Register Bits
MC68302 USER’S MANUAL
Name
NOTE
System Integration Block (SIB)
3.8.2, 3.8.3, 3.8.5
3.8.2, 3.8.6
3.8.3, 3.8.4
3.8.3, 3.8.4
Section(s)
3.8.2
3.8.2
3.8.2
3.8.4
3.8.3
3.8.3
3.8.3
3.8.8
3.8.8
3.8.8
3.8.6
3.8.6
3.8.7
3.8.7
3.8.7
3.8.7
3.9
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