MPC555
/
MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-36
3.12 Instruction Timing
The MPC555 / MPC556 processor is pipelined. Because the processing of an instruc-
tion is broken into a series of stages, an instruction does not require the entire resourc-
es of the processor.
The instruction pipeline in the MPC555 / MPC556 has four stages:
1. The dispatch stage is implemented using a distributed mechanism. The central
dispatch unit broadcasts the instruction to all units. In addition, scoreboard in-
formation (regarding data dependencies) is broadcast to each execution unit.
Each execution unit decodes the instruction. If the instruction is not implement-
ed, a program exception is taken. If the instruction is legal and no data depen-
dency is found, the instruction is accepted by the appropriate execution unit,
and the data found in the destination register is copied to the history buffer. If a
data dependency exists, the machine is stalled until the dependency is re-
solved.
Table 3-21 Exception Vector Offset Table
Vector Offset
(Hexadecimal)
Exception Type
00000
Reserved
00100
System reset, NMI interrupt
00200
Machine check
00300
Reserved
00400
Reserved
00500
External interrupt
00600
Alignment
00700
Program
00800
Floating-point unavailable
00900
Decrementer
00A00
Reserved
00B00
Reserved
00C00
System call
00D00
Trace
00E00
Floating-point assist
01000
Implementation-dependent software emulation
01100
Reserved
01200
Reserved
01300
Implementation-dependent instruction protection error
01400
Implementation-dependent data protection error
01500–01BFF
Reserved
01C00
Implementation-dependent data breakpoint
01D00
implementation-dependent instruction breakpoint
01E00
Implementation-dependent maskable external breakpoint
01F00
Implementation-dependent non-maskable external breakpoint
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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