MPC555 / MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-1
SECTION 3
CENTRAL PROCESSING UNIT
The PowerPC-based RISC processor (RCPU) used in the MPC500 family of micro-
controllers integrates five independent execution units: an integer unit (IU), a load/
store unit (LSU), and a branch processing unit (BPU), floating-point unit (FPU) and in-
teger multiplier divider (IMD). The use of simple instructions with rapid execution times
yields high efficiency and throughput for MPC555 / MPC556-based systems.
Most integer instructions execute in one clock cycle. Instructions can complete out of
order for increased performance; however, the processor makes execution appear se-
quential.
This section provides an overview of the RCPU. For a detailed description of this pro-
cessor, refer to the
RCPU Reference Manual
(RCPURM/AD)
.
3.1 RCPU Features
Major features of the RCPU include the following:
• High-performance microprocessor
— Single clock-cycle execution for many instructions
• Five independent execution units and two register files
— Independent LSU for load and store operations
— BPU featuring static branch prediction
— A 32-bit IU
— Fully IEEE 754-compliant FPU for both single- and double-precision opera-
tions
— Thirty-two general-purpose registers (GPRs) for integer operands
— Thirty-two floating-point registers (FPRs) for single- or double-precision oper-
ands
• Facilities for enhanced system performance
— Programmable big- and little-endian byte ordering
— Atomic memory references
• In-system testability and debugging features
• High instruction and data throughput
— Condition register (CR) look-ahead operations performed by BPU
— Branch-folding capability during execution (zero-cycle branch execution time)
— Programmable static branch prediction on unresolved conditional branches
— A pre-fetch queue that can hold up to four instructions, providing look-ahead
capability
— Interlocked pipelines with feed-forwarding that control data dependencies in
hardware
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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