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3.2 CPU Register Descriptions
3.2.1 General Registers
All eight of the 16-bit general registers are functionally alike; there is no distinction between data
registers and address registers. When these registers are accessed as data registers, either byte or
word size can be selected.
R6 and R7, in addition to functioning as general registers, have special assignments.
R7 is the stack pointer, used implicitly in exception handling and subroutine calls. It can be
designated by the name SP, which is synonymous with R7. As indicated in figure 3-3, it points to
the top of the stack. It is also used implicitly by the LDM and STM instructions, which load and
store multiple registers from and to the stack and pre-decrement or post-increment R7 accordingly.
R6 functions as a frame pointer (FP). The LINK and UNLK use R6 implicitly to reserve or
release a stack frame.
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SP
Figure 3-3 Stack Pointer
Unused area
Stack area
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