MVN

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). No flags are affected.

In Eyes & Lichty, the "N" in the mnemonic stands for "Next" not "Negative."

MVN works even in emulation mode, but the blocks must be in the zeropage.

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

If interrupted, the current byte finishes copying before servicing the interrupt. The destination bank is written to DBR.

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

• MVP
• DMA

External Links

• Eyes & Lichty, page 466 on MVN
• Labiak, page 153 on MVN
• 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
• Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.6

References

1. https://github.com/InsaneFirebat/sm_practice_hack/blob/master/src/custompresets.asm#L260