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MVN
From SnesLab
| Basic Info | |||||||
|---|---|---|---|---|---|---|---|
| Addressing Mode | Opcode | Length | Speed | ||||
| block move | 54 | 3 bytes | 7 cycles per byte moved | ||||
| Flags Affected | ||||||||
|---|---|---|---|---|---|---|---|---|
| N | V | M | X | D | I | Z | C | |
| . | . | . | . | . | . | . | . | |
MVN (Block Move Negative) is a 65c816 instruction that copies a contiguous block of memory. It is intended to copy a block from a higher address to a lower address (moving it in the negative direction).
In Eyes & Lichty, the "N" in the mnemonic stands for "Next" not "Negative."
Parameters
- the X index register specifies the starting (lowest) source address of the block
- the Y index register specifies the starting (lowest) destination address of the block
- the C double accumulator specifies the length of the block in bytes minus one
- the first operand byte specifies the destination bank the block will be in
- the second operand byte specifies the source bank the block starts out in
Execution Sequence
The following loop is repeated until the value in the C double accumulator is $FFFF:
- one byte is copied from the address in X to the address in Y
- both X and Y are incremented
- C is decremented
Assembler Syntax
Asar:
MVN srds
where "sr" is the source bank, and "ds" is the destination bank, with nothing in between them.[1]
See Also
External Links
- Eyes & Lichty page on MVN: https://archive.org/details/0893037893ProgrammingThe65816/page/n492
- Labiak page 153 on MVN: https://archive.org/details/Programming_the_65816/page/n163
- snes9x implementation of MVN: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3011
- undisbeliever on MVN: https://undisbeliever.net/snesdev/65816-opcodes.html#mvn-block-move-next