STY

Basic Info
Addressing Mode	Opcode	Length	Speed
Absolute	8C	3 bytes	4 cycles*
Direct Page	84	2 bytes	3 cycles*
Direct Page Indexed by X	94	2 bytes	4 cycles*

Flags Affected
N	V	M	X	D	I	Z	C
.	.	.	.	.	.	.	.

STY (Store Y) is a 65x instruction that stores the value of the Y index register.

No flags are affected.

Syntax

STY addr
STY dp
STY dp, X

Cycle Penalties

• STY takes one additional cycle when the index registers are 16 bits wide, in all addressing modes.
• In both direct page addressing modes only, STY takes another additional cycle if the low byte of the direct page register is nonzero.

See Also

• LDY
• STA
• STX
• STZ
• TYA
• TYX

External Links

• Eyes & Lichty page 506, on STY: https://archive.org/details/0893037893ProgrammingThe65816/page/506
• Labiak page 187 on STY: https://archive.org/details/Programming_the_65816/page/n197
• MCS6500 Manual page 97 on STY: https://archive.org/details/mos_microcomputers_programming_manual/page/n115
• Carr page 274 on STY: https://archive.org/details/6502UsersManual/page/n287
• Leventhal page 3-98 on STY: https://archive.org/details/6502-assembly-language-programming/page/n147
• snes9x implementation of STY: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1302
• undisbeliever on STY: https://undisbeliever.net/snesdev/65816-opcodes.html#sty-store-index-register-y-to-memory