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|[[Immediate]]
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|3 cycles*
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|[[Absolute Indexed by X]]
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|[[Direct Page Indexed by X]]
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|[[Negative Flag|N]]
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|M
|[[M Flag|M]]
|X
|[[X Flag|X]]
|D
|[[Decimal Flag|D]]
|I
|[[I Flag|I]]
|Z
|[[Zero Flag|Z]]
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|[[Carry Flag|C]]
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|[[Immediate]]
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'''BIT''' is a 65x instruction that performs a logical AND operation between the [[accumulator]] and memory without storing the conjunction.
'''BIT''' is a 65x instruction that performs a logical AND operation between the [[accumulator]] and memory without storing the conjunction.  If the conjunction is zero, the [[zero flag]] is set, otherwise it is cleared.
 
Except in [[immediate addressing]], the most significant bit of the data located at the effective address is moved into the [[negative flag]], and the second most significant bit of that data is moved into the [[overflow flag]].  BIT is often used right before a conditional branch instruction like [[BVC]] or [[BVS]].


Except in [[immediate addressing]], the most significant bit of the data located at the effective address is moved into the [[negative flag]], and the second most significant bit of that data is moved into the [[overflow flag]].
==== Syntax ====
<pre>
BIT #const
BIT addr
BIT dp
BIT addr, X
BIT dp, X
</pre>


===== Cycle Penalties =====
==== Cycle Penalties ====
* BIT takes an extra cycle when the accumulator is 16 bits wide, in all [[addressing modes]]
* BIT takes an extra cycle when the accumulator is 16 bits wide, in all [[addressing modes]]
* In direct page addressing modes, BIT takes an extra cycle when the low byte of the [[direct page register]] is nonzero
* In direct page addressing modes, BIT takes an extra cycle when the low byte of the [[direct page register]] is nonzero
* In [[Absolute Indexed, X Addressing]], BIT takes an extra cycle when adding the index crosses a page boundary
* In [[Absolute Indexed, X Addressing]], BIT takes an extra cycle when adding the index crosses a [[page]] boundary


=== See Also ===
=== See Also ===
* [[AND]]
* [[AND]]
* [[BPL]]
* [[BNE]]
* [[BCC]]
* [[BCS]]


=== External Links ===
=== External Links ===
* [[Eyes & Lichty]] page 431, on BIT: https://archive.org/details/0893037893ProgrammingThe65816/page/n457
* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/431 page 431] on BIT
* [[Labiak]] page on BIT: https://archive.org/details/Programming_the_65816/page/n131
* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n131 page 121] on BIT
* [[MCS6500 Manual]] page on BIT: https://archive.org/details/mos_microcomputers_programming_manual/page/n62
* 4.2.2.1 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n62 page 47] on BIT
* [[Carr]] page on BIT: https://archive.org/details/6502UsersManual/page/n262
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n262 page 249] on BIT
* [[Leventhal]] page on BIT: https://archive.org/details/6502-assembly-language-programming/page/n94
* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n94 page 3-45] on BIT
* snes9x implementation of BIT: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L265
* snes9x implementation of BIT: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L265
* undisbeliever on BIT: https://undisbeliever.net/snesdev/65816-opcodes.html#bit-test-memory-bits-against-accumulator
* undisbeliever on BIT: https://undisbeliever.net/snesdev/65816-opcodes.html#bit-test-memory-bits-against-accumulator
* Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#BIT
* Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.2.2


[[Category:ASM]]
[[Category:ASM]]
[[Category:Group Three Instructions]]
[[Category:Group Three Instructions]]
[[Category:Inherited from 6502]]
[[Category:Inherited from 6502]]

Latest revision as of 17:48, 23 August 2024

Basic Info
Addressing Mode Opcode Length Speed
Immediate 89 2/3 bytes 2 cycles*
Absolute 2C 3 bytes 4 cycles*
Direct Page 24 2 bytes 3 cycles*
Absolute Indexed by X 3C 3 bytes 4 cycles*
Direct Page Indexed by X 34 2 bytes 4 cycles*
Flags Affected
Addressing Mode N V M X D I Z C
Immediate . . . . . . Z .
other N V . . . . Z .

BIT is a 65x instruction that performs a logical AND operation between the accumulator and memory without storing the conjunction. If the conjunction is zero, the zero flag is set, otherwise it is cleared.

Except in immediate addressing, the most significant bit of the data located at the effective address is moved into the negative flag, and the second most significant bit of that data is moved into the overflow flag. BIT is often used right before a conditional branch instruction like BVC or BVS.

Syntax

BIT #const
BIT addr
BIT dp
BIT addr, X
BIT dp, X

Cycle Penalties

See Also

External Links

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