We've just updated MediaWiki and its underlying software. If anything doesn't look or work quite right, please mention it to us. --RanAS
STZ: Difference between revisions
From SnesLab
(added 65c02 additions category) |
(→External Links: storing zero to memory) |
||
(18 intermediate revisions by the same user not shown) | |||
Line 1: | Line 1: | ||
{| class="wikitable" style="float:right;clear:right;width:40%" | |||
{| class="wikitable" style="width: | |||
!colspan="8"|Basic Info | !colspan="8"|Basic Info | ||
|+ | |+ | ||
Line 9: | Line 7: | ||
|'''Speed''' | |'''Speed''' | ||
|+ | |+ | ||
| | |[[Absolute]] | ||
|9C | |9C | ||
|3 bytes | |3 bytes | ||
|4 cycles | |4 cycles* | ||
|+ | |+ | ||
| | |[[Direct Page Addressing|Direct Page]] | ||
|64 | |64 | ||
|2 bytes | |2 bytes | ||
|3 cycles | |3 cycles* | ||
|+ | |+ | ||
|absolute indexed X | |absolute indexed X | ||
|9E | |9E | ||
|3 bytes | |3 bytes | ||
|5 cycles | |5 cycles* | ||
|+ | |+ | ||
|direct page indexed X | |direct page indexed X | ||
|74 | |74 | ||
|2 bytes | |2 bytes | ||
|4 cycles | |4 cycles* | ||
|} | |} | ||
{| class="wikitable" style="float:right;clear:right;width:30%" | {| class="wikitable" style="float:right;clear:right;width:30%" | ||
!colspan="9"|Flags | !colspan="9"|Flags Affected | ||
|+ | |+ | ||
|N | |[[Negative Flag|N]] | ||
|V | |[[Overflow Flag|V]] | ||
|M | |[[M Flag|M]] | ||
|X | |[[X Flag|X]] | ||
|D | |[[Decimal Flag|D]] | ||
|I | |[[I Flag|I]] | ||
|Z | |[[Zero Flag|Z]] | ||
|C | |[[Carry Flag|C]] | ||
|+ | |+ | ||
|. | |. | ||
Line 51: | Line 49: | ||
|. | |. | ||
|} | |} | ||
'''STZ''' (Store Zero) is a [[65c816]] instruction that zeros out memory. The size of the [[accumulator]] determines how many zero bytes are written. | |||
===== Cycle Penalties ===== | |||
* STZ takes one additional cycle if the accumulator is 16 bits wide, in all [[addressing modes]]. | |||
* In [[direct page addressing]] modes only, STZ takes another additional cycle if the low byte of the [[direct page register]] is nonzero. | |||
=== See Also === | === See Also === | ||
Line 56: | Line 60: | ||
* [[STX]] | * [[STX]] | ||
* [[STY]] | * [[STY]] | ||
=== External Links === | |||
* [[Eyes & Lichty]] page 507, on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533 | |||
* "Storing Zero to Memory," page 103, lbid. https://archive.org/details/0893037893ProgrammingThe65816/page/n129 | |||
* [[Labiak]] page 188 on STZ: https://archive.org/details/Programming_the_65816/page/n198 | |||
* snes9x implementation of STZ: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1317 | |||
* undisbeliever on STZ: https://undisbeliever.net/snesdev/65816-opcodes.html#stz-store-zero-to-memory | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:65c02 additions]] | [[Category:65c02 additions]] | ||
[[Category:Load/Store Instructions]] |
Latest revision as of 13:52, 14 December 2023
Basic Info | |||||||
---|---|---|---|---|---|---|---|
Addressing Mode | Opcode | Length | Speed | ||||
Absolute | 9C | 3 bytes | 4 cycles* | ||||
Direct Page | 64 | 2 bytes | 3 cycles* | ||||
absolute indexed X | 9E | 3 bytes | 5 cycles* | ||||
direct page indexed X | 74 | 2 bytes | 4 cycles* |
Flags Affected | ||||||||
---|---|---|---|---|---|---|---|---|
N | V | M | X | D | I | Z | C | |
. | . | . | . | . | . | . | . |
STZ (Store Zero) is a 65c816 instruction that zeros out memory. The size of the accumulator determines how many zero bytes are written.
Cycle Penalties
- STZ takes one additional cycle if the accumulator is 16 bits wide, in all addressing modes.
- In direct page addressing modes only, STZ takes another additional cycle if the low byte of the direct page register is nonzero.
See Also
External Links
- Eyes & Lichty page 507, on STZ: https://archive.org/details/0893037893ProgrammingThe65816/page/n533
- "Storing Zero to Memory," page 103, lbid. https://archive.org/details/0893037893ProgrammingThe65816/page/n129
- Labiak page 188 on STZ: https://archive.org/details/Programming_the_65816/page/n198
- snes9x implementation of STZ: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1317
- undisbeliever on STZ: https://undisbeliever.net/snesdev/65816-opcodes.html#stz-store-zero-to-memory