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CHAPTER 3 REGISTER DESCRIPTIONS
Figure 3.3-13 Example of Stack Pointer Operation in Execution of Instruction "ST R13, @-R15"
when "S" Flag = 1
■ Stack Pointer Configuration
Figure 3.3-14 shows the bit configuration of the stack pointer.
Figure 3.3-14 Bit Configuration of the Stack Pointers
■ Functions of the System Stack Pointer and User Stack Pointer
● Automatic increment/decrement of stack pointer
The stack pointer uses automatic pre-decrement/post-increment counting.
● Stack Pointer Initial Value
The "SSP" has the initial value "00000000
H
". The "USP" initial value is undefined.
■ Recovery from EIT handler
When RETI instruction is used for recovery from an EIT handler, it is necessary to set the "S" flag to "0"
and select the system stack. For further details, see "
■ Recovery from EIT handler" of "4.2 Basic
Operations in "EIT" Processing".
Memory space
????????
????????
Before execution of ST R13,@-R15
12345678
H
76543210H
SSP
USP
17263540
H
1
R13
CCR
FFFFFFFF
H
After execution of ST R13,@-R15
12345678
H
7654320CH
SSP
USP
17263540
H
17263540H
1
R13
CCR
SS
00000000
H
Memory space
FFFFFFFF
H
00000000H
Bit no.
SSP
USP
31
00