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ADDRESS SPACES
S3C9454B/F9454B
2-8
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.
Stack contents
after a call
instruction
Stack contents
after an
interrupt
Top of
stack
Flags
PCH
PCL
PCL
PCH
Top of
stack
Low Address
High Address
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.
Содержание S3C9454B
Страница 1: ...S3C9454B F9454B 8 BIT CMOS MICROCONTROLLER USER S MANUAL Revision 1 ...
Страница 25: ...PRODUCT OVERVIEW S3C9454B F9454B 1 10 NOTES ...
Страница 35: ...ADDRESS SPACES S3C9454B F9454B 2 10 NOTES ...
Страница 65: ...CONTROL REGISTERS S3C9454B F9454B 4 18 NOTES ...
Страница 123: ...CLOCK CIRCUIT S3C9454B F9454B 7 4 NOTES ...
Страница 133: ...RESET and POWER DOWN S39454B F9454B 8 10 NOTES ...
Страница 145: ...I O PORTS S3C9454B F9454B 9 12 NOTES ...
Страница 173: ...A D CONVERTER S3C9454B F9454B 12 8 NOTES ...
Страница 183: ...ELECTRICAL DATA S3C9454B F9454B 13 10 NOTES ...
Страница 193: ...S3F9454B MTP S3C9454B F9454B 15 4 NOTES ...