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CHAPTER 2 CPU
MB90560 series
2.9
2.9.1 Bank select prefix (PCB, DTB, ADB, SPB)
Prefix Codes
A bank select prefix is placed before an instruction to select the memory space
accessed by the instruction regardless of the addressing method.
I
Bank select prefixes (PCB, DTB, ADB, SPB)
The memory space used for data access is defined for each addressing method. If a bank select
prefix is placed before an instruction, the memory space accessed by the instruction can be
selected regardless of the addressing method. Table 2.9-1 lists the bank select prefix codes and
selected memory spaces.
Table 2.9-1 Bank select prefix codes and selected memory spaces
If a bank select prefix is used, some instructions perform an unexpected operation.
Table 2.9-2 lists the instructions that are not affected by bank select prefix codes. Table 2.9-3
lists instructions that require caution when they are used.
Table 2.9-2 Instructions not affected by bank select prefix codes
Bank select prefix
Selected space
PCB
DTB
ADB
Program space
Data space
Additional space
When the value of the S flag in the condition code register (CCR) is
0 and the user stack space is 1, the system stack space is used.
SPB
Instruction
type
Instruction
Effect of bank select prefix
String
instruction
MOVS
SCEQ
FILS
MOVSW
SCWEQ
FILSW
The bank register specified by the operand is
used regardless of whether a prefix is used.
Stack opera-
tion
PUSHW
POPW
When the S flag is “0”, the user stack bank
(USB) is used regardless of whether there is
a prefix. When the S flag is “1”, the system
stack bank (SSB) is used regardless of
whether a prefix is used.]
I/O access
instruction
MOV
MOVW A, io
MOV
MOV
MOVB
SETB
BBC
WBTC
A
MOVX
A, io
io, A
io, #imm8
A, io : bp
io : bp
io : bp, rel
io, bp
MOVW
MOVW
MOVB
CLRB
BBS
WBTS
io, A
io, #imm16
io : bp, A
io : bp
io : bp, rel
io : bp
The I/O space (“000000
H
“ to “0000FF
H
”) is
accessed regardless of whether there is a
prefix.
Interrupt
return
instruction
RETI
The system stack bank (SSB) is used
regardless of whether a prefix is used.