Section 2 CPU
Rev. 3.00 Sep. 27, 2007 Page 24 of 758
REJ09B0243-0300
Load/Store Architecture:
Basic operations are executed between registers. In operations
involving memory, data is first loaded into a register (load/store architecture). However, bit
manipulation instructions such as AND are executed directly in memory.
Delayed Branching:
Unconditional branch instructions means the delayed branch instructions.
With a delayed branch instruction, the branch is made after execution of the instruction
immediately following the delayed branch instruction. This minimizes disruption of the pipeline
when a branch is made. The conditional branch instructions have two types of instructions:
conditional branch instructions and delayed branch instructions.
Table 2.3
Delayed Branch Instructions
CPU in this LSI
Description
Example of Other CPUs
BRA TRGET
ADD R1,R0
ADD is executed before branch to TRGET.
ADD.W R1,R0
BRA TRGET
Multiply/Multiply-and-Accumulate Operations:
A 16
×
16
→
32 multiply operation is
executed in one to two cycles, and a 16
×
16 + 64
→
64 multiply-and-accumulate operation in two
to three cycles. A 32
×
32
→
64 multiply operation and a 32
×
32 + 64
→
64 multiply-and-
accumulate operation are each executed in two to four cycles.
T Bit:
The result of a comparison is indicated by the T bit in SR, and a conditional branch is
performed according to whether the result is True or False. Processing speed has been improved
by keeping the number of instructions that modify the T bit to a minimum.
Table 2.4
T Bit
CPU in this LSI
Description
Example of Other CPUs
CMP/GE R1,R0
When
R0
≥
R1, the T bit is set.
CMP.W R1,R0
BT TRGET0
When
R0
≥
R1, a branch is made to TRGET0. BGE
TRGET0
BF
TRGET1
When R0 < R1, a branch is made to TRGET1. BLT
TRGET1
ADD #
1,R0
The T bit is not changed by ADD.
SUB.W #1,R0
CMP/EQ #0,R0
When R0 = 0, the T bit is set.
BEQ
TRGET
BT
TRGET
A branch is made when R0 = 0.
Immediate Data:
8-bit immediate data is placed in the instruction code. Word and longword
immediate data is not placed in the instruction code. It is placed in a table in memory. The table in
memory is accessed with the MOV immediate data instruction using PC relative addressing mode
with displacement.
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