S3C72G9 Просмотр технического описания (PDF) - Samsung
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S3C72G9 Datasheet PDF : 96 Pages
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REDUCING INSTRUCTION REDUNDANCY
When redundant instructions such as LD A,#im and LD EA,#imm are used consecutively in a program sequence,
only the first instruction is executed. The redundant instructions which follow are ignored, that is, they are handled
like a NOP instruction. When LD HL,#imm instructions are used consecutively, redundant instructions are also
ignored.
In the following example, only the 'LD A, #im' instruction will be executed. The 8-bit load instruction which follows it
is interpreted as redundant and is ignored:
LD
A,#im
LD
EA,#imm
; Load 4-bit immediate data (#im) to accumulator
; Load 8-bit immediate data (#imm) to extended
; accumulator
In this example, the statements 'LD A,#2H' and 'LD A,#3H' are ignored:
BITR
LD
LD
LD
LD
EMB
A,#1H
A,#2H
A,#3H
23H,A
; Execute instruction
; Ignore, redundant instruction
; Ignore, redundant instruction
; Execute instruction, 023H ← #1H
If consecutive LD HL, #imm instructions (load 8-bit immediate data to the 8-bit memory pointer pair, HL) are
detected, only the first LD is executed and the LDs which immediately follow are ignored. For example,
LD
HL,#10H
LD
HL,#20H
LD
A,#3H
LD
EA,#35H
LD
@HL,A
; HL ← 10H
; Ignore, redundant instruction
; A ← 3H
; Ignore, redundant instruction
; (10H) ← 3H
If an instruction reference with a REF instruction has a redundancy effect, the following conditions apply:
— If the instruction preceding the REF has a redundancy effect, this effect is cancelled and the referenced
instruction is not skipped.
— If the instruction following the REF has a redundancy effect, the instruction following the REF is skipped.
PROGRAMMING TIP — Example of the Instruction Redundancy Effect
ABC
ORG
LD
ORG
LD
REF
REF
LD
0020H
EA,#30H
0080H
EA,#40H
ABC
ABC
EA,#50H
; Stored in REF instruction reference area
; Redundancy effect is encountered
; No skip (EA ← #30H)
; EA ← #30H
; Skip
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