Prefix Codes - Fujitsu MB90335 Series Hardware Manual

CHAPTER 2 CPU

2.8 Prefix Codes

2.8 Prefix Codes
Placing a prefix code before an instruction can partially change the operation of the
instruction. 3 types of prefix codes can be used: bank select prefix, common register
bank prefix, and flag change disable prefix.
■ Bank Select Prefix
The memory space used for accessing data depends on each addressing mode. When a bank select prefix is
placed before an instruction, the memory space used for accessing data by that instruction can be selected
regardless of the addressing mode.
Table 2.8-1 shows the bank select prefixes and selected memory spaces.
Table 2.8-1 Bank Select Prefix
Bank select prefix
PCB
DTB
ADB
SPB
Use the following instructions with care:
●
String instructions (MOVS / MOVSW / SCEQ / SCWEQ / FILS / FILSW)
The bank register specified by an operand is used regardless of the prefix.
●
Stack manipulation instructions (PUSHW / POPW)
SSB or USB is used according to the S flag regardless of the prefix.
●
I/O access instructions
MOV A,io
MOV io,#imm8
CLRB io:bp
The I/O space of the bank is used regardless of the prefix.
●
Flag change instructions (AND CCR,#imm8 / OR CCR,#imm8)
The instruction is executed normally, but the prefix affects the next instruction.
40
PC space
Data space
AD space
Either the SSP or USP space is used according to the stack flag value.
MOV io,A
MOVW io,#imm16
BBC io:bp,rel
FUJITSU MICROELECTRONICS LIMITED
Selected space
MOVX A,io MOVW A,io
MOVB A,io:bp MOVB io:bp,A
BBS io:bp,rel WBTC
MB90335 Series
MOVW io,A
SETB io:bp
WBTS
CM44-10137-6E