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CHAPTER 3 CPU
3.4
Prefix Code
When prefix code is inserted by an instruction, the operation of the instruction can be
changed partially. The prefix code has the following three types:
• Bank select prefix (PCB, DTB, ADB, and SPB)
• Common register bank prefix (CMR)
• Flag change inhibit prefix (NCC)
I Prefix Code
G
Bank select prefix (PCB, DTB, ADB, and SPB)
When the bank select prefix (PCB, DTB, ADB, SPB) codes precede an instruction, any memory space to
be accessed by the instruction can be selected, regardless of the addressing types.
G
Common register bank prefix (CMR)
When the common register bank prefix (CMR) code precedes an instruction for accessing a general-
purpose register, the general-purpose register to be accessed by the instruction can be changed to a common
bank (register bank selected when the register bank pointer (RP) is 0) at 000180
the current value of the register bank pointer (RP).
G
Flag change inhibit prefix (NCC)
When the flag change inhibit (NCC) code precedes an instruction for changing various flags of the
condition code register (CCR), a flag change with instruction execution can be inhibited.
50
to 00018F
, regardless of
H
H
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