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❍ Return pointer (RP)
31
RP
The return pointer holds the address returned from a subroutine.
When a CALL instruction is executed, the PC value is transferred to this RP.
When a RET instruction is executed, the RP contents are transferred to PC.
The initial value after reset is undefined.
❍ System stack pointer (SSP)
31
SSP
SSP is the system stack pointer.
SSP functions as R15 when the S flag is 0.
SSP can also be specified explicitly.
This register is also used as a stack pointer that specifies the stack on which the PS and PC
contents are to be saved if an EIT occurs.
The initial value after reset is 00000000
❍ User stack pointer (USP)
31
USP
USP is the user stack pointer
USP functions as R15 when the S flag is 1.
USP can also be specified explicitly.
The initial value after reset is undefined.
This register cannot be used by the RETI instruction.
CHAPTER 3 CPU AND CONTROL UNITS
0 [Initial value]
XXXXXXXX
0 [Initial value]
00000000
.
H
0 [Initial value]
XXXXXXXX
H
H
H
41
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