Flag Change Inhibit Prefix (Ncc) - Fujitsu MB90895 Series Hardware Manual

CHAPTER 3 CPU
3.4.3

Flag change inhibit prefix (NCC)

When the flag change inhibit prefix (NCC) code precedes an instruction for changing
various flags of the condition code register (CCR), a flag change caused by instruction
execution can be inhibited.
I Flag change inhibit prefix (NCC)
The flag change inhibit prefix (NCC) code is used to inhibit an unnecessary flag change.
When the flag change inhibit prefix (NCC) code precedes an instruction for changing various flags of the
condition code register (CCR), a flag change caused by instruction execution can be inhibited.
• Sticky-bit flag (CCR: T)
• Negative flag (CCR: N)
• Zero flag (CCR: Z)
• Overflow flag (CCR: V)
• Carry flag (CCR: C)
Table 3.4-5 shows the instructions requiring precaution when using the flag change inhibit prefix.
Table 3.4-5 Instructions Requiring Precaution When Using Flag Change Inhibit Prefix (NCC)
Instruction Types
String instruction
Flag change instruction
PS Return instruction
ILM setting instruction
Interrupt instruction
Interrupt return instruction
Context switch instruction
54
Instruction
MOVS MOVSW
SCEQ SCWEQ
FILS FILSW
AND CCR,#imm8
OR CCR,#imm8
POPW PS
MOV ILM,#imm8
INT #vct8 INT9
INT addr16 INTP addr24
RETI
JCTX @A
Do not the add the NCC code to the string instruction.
The CCR changes by execution of an instruction, regardless of the
presence or absence of the NCC code.
The flag change inhibit prefix code affects the next instruction.
The CCR changes by execution of an instruction, regardless of the
presence or absence of the NCC code.
The flag change inhibit prefix code affects the next instruction.
The flag change inhibit prefix code affects up to the next instruction.
The CCR changes by execution of an instruction, regardless of the
presence or absence of the NCC code.
The CCR changes by execution of an instruction, regardless of the
presence or absence of the NCC code.
Description