Central Processing Unit
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
3-21
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. Little-endian mode is not
supported on the MPC561/MPC563. This bit should be cleared to 0 at all times.
0 The processor runs in big-endian mode during exception processing.
1 The 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).
Software should disable interrupts (EE = 0) in the RCPU before clearing or masking any
interrupt source from the USIU or external pins. For external interrupts, it is recommended that
the edge-triggered interrupt scheme be used. See
Section 6.1.4, “Enhanced Interrupt
.”
0 The processor delays recognition of external interrupts and decrementer exception
conditions.
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
exception 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 when the next instruction executes
successfully. When this bit is set, the processor dispatches instructions in strict program
order. Successful execution means the instruction caused no other exception.
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.
Table 3-11. Machine State Register Bit Descriptions (continued)
Bits
Name
Description
Summary of Contents for MPC561
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