S3C9454B View Datasheet(PDF) - Samsung
Part Name
Description
MFG CO.
'S3C9454B' PDF : 199 Pages View PDF
ADDRESS SPACES
S3C9454B/F9454B
SYSTEM STACK
S3C9-series microcontrollers use the system stack for subroutine calls and returns and to store data. The PUSH
and POP instructions are used to control system stack operations. The S3C9454B/F9454B architecture supports
stack operations in the internal register file.
Stack Operations
Return addresses for procedure calls and interrupts and data are stored on the stack. The contents of the PC are
saved to stack by a CALL instruction and restored by the RET instruction. When an interrupt occurs, the contents
of the PC and the FLAGS register are pushed to the stack. The IRET instruction then pops these values back to
their original locations. The stack address is always decremented before a push operation and incremented after a
pop operation. The stack pointer (SP) always points to the stack frame stored on the top of the stack, as shown in
Figure 2-5.
Top of
stack
High Address
PCL
PCH
Stack contents
after a call
instruction
Top of
stack
Low Address
PCL
PCH
Flags
Stack contents
after an
interrupt
Figure 2-5. Stack Operations
Stack Pointer (SP)
Register location D9H contains the 8-bit stack pointer (SP) that is used for system stack operations. After a reset,
the SP value is undetermined.
Because only internal memory space is implemented in the S3C9454B/F9454B, the SP must be initialized to an 8-
bit value in the range 00H–0C0H.
NOTE
In case a Stack Pointer is initialized to 00H, it is decreased to FFH when stack operation starts. This
means that a Stack Pointer access invalid stack area. We recommend that a stack pointer is initialized to
C0H to set upper address of stack to BFH.
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