2.6.11 I0 to IE Index registers
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How index registers work
● Index registers are used to indirectly specify constants and memory area addresses.
● Depending on the values of the index register, changes to addresses and constants are
called "index modification".
● Fifteen 32-bit registers are available for I0 to IE.
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Notes on using index registers
● When the result of an address modifier exceeds the range for the memory area, an operation
error occurs.
Example) When the result of the modifier is an address with a negative value or value that is
too large
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Values that can be modified with index registers
● Number of the memory area used for a basic instruction
● Slot number or memory area number
● Number of the memory area used for a high-level instruction
● Value of the constant specified for a high-level instruction
● K constant (16-bit, 32-bit)
● U constant (16-bit, 32-bit)
● H constant (16-bit, 32-bit)
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Value that cannot be modified with index registers
● Floating point data
● Depending on the instruction, index modification cannot be applied to some operands. Refer
to the "Available devices" section of the description page for each instruction.
● An index register (I0 to IE) occupies a 32-bit area.
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How to apply index modification
<Example 1> Modifying a transfer destination
The address in the data register (DT) for the transfer destination varies according to the value
of DT0.
2.6 Description of the memory area
2-36 WUME-FP7CPUPGR-12
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