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USP (User Stack Pointer)
USP
The USP is a user stack pointer.
It serves as R15 of the general-purpose register when the S-flag contains "1".
The USP can be explicitly specified.
The initial value after a reset is indeterminate.
This pointer cannot be used by the RETI instruction.
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Multiply & Divide registers : MDH, MDL
MDH
MDL
These registers hold the results of a multiplication or division. Each of them is 32 bits long.
The initial value after a reset is indeterminate.
When a multiplication is performed:
The operation result of a multiplication of 32 bits × 32 bits is 64 bits long, which are stored in the
multiply & divide result storage registers as follows:
MDH: Upper 32 bits
MDL: Lower 32 bits
The result of a 16 × 16-bit multiplication is stored as follows:
MDH: Indeterminate
MDL: Result of 32 bits long
When a division is performed:
The dividend is stored in the MDL at the start of the calculation.
When the division is performed by the DIV0S/DIV0U, DIV1, DIV2, DIV3, or DIV4S instruction, the
results are stored in the MDL and MDH as follows:
MDH: Remainder
MDL: Quotient
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CHAPTER 3 CPU AND CONTROL UNITS
0
[Initial value]
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H
0
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