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How to designate the ISP as the stack pointer in user mode?

Latest Updated:06/20/2013

Question:

I wish to designate the ISP as the stack pointer in user mode. Are there any problems associated with doing this, and is there anything I need to be careful of?

Answer:

The ISP cannot be designated to the stack pointer in user mode.
At initial settings, the processor mode is supervisor mode. When switching from supervisor mode to user mode, the U bit in the PSW register is automatically set to 1, and the USP is designated as the stack pointer.
In addition, the U bit in the PSW register cannot be changed in user mode. There, the ISP cannot be designated to the stack pointer in user mode.
For more information on the stack pointer designation bits (U) of the ISP, USP, and PSW registers, please refer to the "Register Set" section in the "CPU" chapter of the hardware manual.
For more information on processor modes, please refer to the "Processor Mode" section in the "CPU" chapter of the hardware manual.
For more information on exception sequences, please refer to the "Exceptions" chapter of the hardware manual."
Suitable Products
RX62N, RX621
RX62T
RX610
RX62G
RX630
RX63N, RX631
RX63T
RX210
RX220
RX110
RX111