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3.9
Prefix Codes
Prefix codes are placed before an instruction to partially change the operation of the
instruction. The three types of prefix codes are as follows:
• Bank select prefix (PCB, DTB, ADB, SPB)
• Common register bank prefix (CMR)
• Flag change suppression prefix (NCC)
■ Prefix Codes
●
Bank select prefix (PCB, DTB, ADB, SPB)
A bank select prefix is placed before an instruction to select the memory space to be accessed by the
instruction regardless of the addressing method.
●
Common register bank prefix (CMR)
The common register bank prefix is placed before an instruction that accesses a register bank to change the
register accessed by the instruction to the common bank (register bank selected when RP = 0) at 000180
to 00018F
●
Flag change suppression prefix (NCC)
The flag change suppression prefix code is placed before an instruction to suppress a flag change
accompanying the execution of the instruction.
regardless of the current register bank pointer (RP) value.
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CHAPTER 3 CPU
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