System Stack Pointer (Ssp) - Fujitsu FR60 Hardware Manual

3.10.3 System Stack Pointer (SSP)

The system stack pointer (SSP) is used to point to the stack to save and restore data
when EIT is accepted or a return operation occurs.
■ System Stack Pointer (SSP)
The system stack pointer (SSP: System Stack Pointer) consists of 32 bits.
Figure 3.10-2 shows the configuration of system stack pointer (SSP) bits.
SSP
Eight is subtracted from the register value during EIT processing and eight is added to the
register value during the return operation from EIT that occurs when the RETI instruction is
executed.
The system stack pointer (SSP) is initialized to 00000000
The SSP is also used as general-purpose register R15 if the S flag in the CCR is set to "0".
■ Interrupt Stack
The value in the PC or PS is saved to or restored from an area pointed to by the system stack
pointer (SSP). After an interrupt occurs, the PC is stored at the address indicated by the SSP
and the PS is stored at the address indicated by the SSP plus 4. This situation is shown in
Figure 3.10-3.
[Example] [Before interrupt]
SSP
Memory
80000000
H
7FFFFFFC
H
7FFFFFF8
H
Figure 3.10-2 Configuration of System Stack Pointer Bit
bit 31 . .
Figure 3.10-3 Interrupt Stack
8 0 0 0 0 0 0 0
H
CHAPTER 3 CPU AND CONTROL UNITS
. . 0 [Initial value]
00000000
by a reset.
H
[After interrupt]
SSP
7 F F F F F F 8
80000000
H
7FFFFFFC
H
7FFFFFF8
H
H
H
PS
PC
83