MPC555
/
MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-21
Table 3-12 Machine State Register Bit Descriptions
Bit(s)
Name
Description
0:12
—
Reserved
13
POW
Power management enable
0 = Power management disabled (normal operation mode)
1 = Power management enabled (reduced power mode)
14
—
Reserved
15
ILE
Exception little-endian mode. When an exception occurs, this bit is copied into MSR[LE] to select
the endian mode for the context established by the exception.
0 = Processor runs in big-endian mode during exception processing.
1 = Processor runs in little-endian mode during exception processing.
16
EE
External interrupt enable. Interrupts should only be negated while the EE bit is disabled (0). Soft-
ware should disable interrupts in the CPU core prior to masking or disabling any interrupt which
might be currently pending at the CPU core. For external interrupts, it is recommended that the
edge triggered interrupt scheme be used.
0 = The processor delays recognition of external interrupts and decrementer exception condi-
tions.
1 = The processor is enabled to take an external interrupt or the decrementer exception.
17
PR
Privilege level
0 = The processor can execute both user- and supervisor-level instructions.
1 = The processor can only execute user-level instructions.
18
FP
Floating-point available
0 = The processor prevents dispatch of floating-point instructions, including floating-point loads,
stores and moves. Floating-point enabled program exceptions can still occur and the FPRs
can still be accessed.
1 = The processor can execute floating-point instructions, and can take floating-point enabled ex-
ception type program exceptions.
19
ME
Machine check enable
0 = Machine check exceptions are disabled.
1 = Machine check exceptions are enabled.
20
FE0
Floating-point exception mode 0 (See
21
SE
Single-step trace enable
0 = The processor executes instructions normally.
1 = The processor generates a single-step trace exception upon the successful execution of the
next instruction. When this bit is set, the processor dispatches instructions in strict program
order. Successful execution means the instruction caused no other exception. Single-step
tracing may not be present on all implementations.
22
BE
Branch trace enable
0 = No trace exception occurs when a branch instruction is completed
1 = Trace exception occurs when a branch instruction is completed
23
FE1
Floating-point exception mode 1 (See
24 —
Reserved
25
IP
Exception prefix. The setting of this bit specifies the location of the exception vector table.
0 = Exception vector table starts at the physical address 0x0000 0000.
1 = Exception vector table starts at the physical address 0xFFF0 0000.
26
IR
Instruction relocation.
0 = Instruction address translation is off, the BBC IMPU does not check for address permission
attributes.
1 = Instruction address translation is on, the BBC IMPU checks for address permission attributes.
27
DR
Data relocation
0 = Data address translation is off, the L2U DMPU does not check for address permission at-
tributes.
1 = Data address translation is on, the L2U DMPU checks for address permission attributes.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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