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2.9
2.9.3 Flag change suppression prefix (NCC)
Prefix Codes
MB90560 series
CHAPTER 2 CPU
63
The flag change suppression prefix (NCC) code is placed before an instruction to
suppress a flag change accompanying the execution of the instruction.
I
Flag change suppression prefix (NCC)
The flag change suppression prefix (NCC) is used to suppress unnecessary flag changes. If a
flag change suppression prefix code is placed before an instruction, a flag change
accompanying the execution of the instruction is suppressed. Changes of the T, N, Z, V, and C
flags are suppressed.
Note that caution is required when this prefix is used with the instructions listed in Table 2.9-5.
Table 2.9-5 Instructions requiring caution when the flag change suppression prefix (NCC)
is used
Instruction
type
Instruction
Explanation
String instruc-
tion
MOVS
SCEQ
FILS
MOVSW
SCWEQ
FILSW
Do not place the NCC prefix before the string
instruction.
Flag change
instruction
AND
CCR, #imm8
OR CCR, #imm8
The condition code register (CCR) changes
as defined in the instruction specification
regardless of whether a prefix is used.
The effect of prefix extends to the next
instruction.
The condition code register (CCR) changes
as defined in the instruction specification
regardless of whether a prefix is used.
The effect of prefix extends to the next
instruction.
The effect of prefix extends to the next
instruction.
PS return
instruction
POPW PS
ILM setting
instruction
Interrupt
instruction
Interrupt
return
instruction
Context
switch
instruction
MOV
ILM, #imm8
INT
INT
RETI
#vct8
adder16
INT9
INTP
addr24
The condition code register (CCR) changes
as defined in the instruction specification
regardless of whether a prefix is used.
JCTX
@A
The condition code register (CCR) changes
as defined in the instruction specification
regardless of whether a prefix is used.