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CHAPTER 2 CPU
MB90560 series
2.9
2.9.2 Common register bank prefix (CMR)
Prefix Codes
The common register bank (CMR) 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
H
to 00018F
H
regardless of the current
register bank pointer (RP) value.
I
Common register bank prefix (CMR)
To facilitate data exchange between multiple tasks, a relatively simple means of accessing a
fixed register bank regardless of the current register bank pointer (RP) value is necessary. This
is the reason that the F
2
MC-16LX provides a common register bank for tasks, which is called the
common bank. The common bank is located at address 000180
H
to 00018F
H
.
If the common register bank prefix (CMR) is placed before an instruction that accesses a register
bank, registers accessed by the instruction can be changed to the common bank (register bank
selected when RP = 0) at 000180
H
to 00018FH
H
regardless of the current register bank pointer
(RP) value.
Note that caution is required when this prefix is used with the instructions listed in Table 2.9-4.
Table 2.9-4 Instructions whose use requires caution when the common register bank
prefix (CMR) is used
Instruction
type
Instruction
Explanation
String instruc-
tion
MOVS
SCEQ
FILS
MOVSW
SCWEQ
FILSW
Do not place the CMR prefix before the string
instruction.
Flag change
instruction
PS return
instruction
ILM setting
instruction
AND
CCR, #imm8
OR CCR, #imm8
The effect of the prefix extends to the next
instruction.
The effect of the prefix extends to the next
instruction.
The effect of the prefix extends to the next
instruction.
POPW PS
MOV
ILM, #imm8