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CMP: Difference between revisions

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'''CMP''' (Compare) is a 65x instruction that compares the value of the [[accumulator]] to something.  Internally, this is done via a subtraction, but the difference is not stored anywhere.  The accumulator serves as the minuend.  CMP only does unsigned comparisons.  In [[immediate addressing]] only, CMP is a total of 3 bytes long when the accumulator is 16 bits wide.  Unlike [[SBC]], the [[carry flag]] does not affect CMP.
'''CMP''' (Compare) is a 65x instruction that compares the value of the [[accumulator]] to something.  Internally, this is done via a subtraction, but the difference is not stored anywhere.  Thus, the purpose of CMP is to setup the flags.  The accumulator serves as the minuend.  CMP only does unsigned comparisons.  In [[immediate addressing]] only, CMP is a total of 3 bytes long when the accumulator is 16 bits wide.  Unlike [[SBC]], the [[carry flag]] does not affect CMP.


If the subtraction required a borrow, the carry flag is cleared (otherwise it is set).
If the subtraction required a borrow, the carry flag is cleared (otherwise it is set).

Revision as of 09:25, 21 July 2024

Basic Info
Addressing Mode Opcode Length Speed
Immediate C9 2/3 bytes 2 cycles*
Absolute CD 3 bytes 4 cycles*
Absolute Long CF 4 bytes 5 cycles*
Direct Page C5 2 bytes 3 cycles*
Direct Page Indirect D2 2 bytes 5 cycles*
Direct Page Indirect Long C7 2 bytes 6 cycles*
Absolute Indexed by X DD 3 bytes 4 cycles*
Absolute Long Indexed by X DF 4 bytes 5 cycles*
Absolute Indexed by Y D9 3 bytes 4 cycles*
Direct Page Indexed by X D5 2 bytes 4 cycles*
Direct Page Indexed Indirect by X C1 2 bytes 6 cycles*
Direct Page Indirect Indexed by Y D1 2 bytes 5 cycles*
Direct Page Indirect Long Indexed by Y D7 2 bytes 6 cycles*
Stack Relative C3 2 bytes 4 cycles*
Stack Relative Indirect Indexed by Y D3 2 bytes 7 cycles*
Flags Affected
N V M X D I Z C
. . . . .

CMP (Compare) is a 65x instruction that compares the value of the accumulator to something. Internally, this is done via a subtraction, but the difference is not stored anywhere. Thus, the purpose of CMP is to setup the flags. The accumulator serves as the minuend. CMP only does unsigned comparisons. In immediate addressing only, CMP is a total of 3 bytes long when the accumulator is 16 bits wide. Unlike SBC, the carry flag does not affect CMP.

If the subtraction required a borrow, the carry flag is cleared (otherwise it is set).

The decimal mode flag has no effect on the behavior of CMP.

Syntax

CMP #const
CMP addr
CMP long
CMP dp
CMP (dp)
CMP [dp]
CMP addr, X
CMP long, X
CMP addr, Y
CMP dp, X
CMP (dp, X)
CMP (dp), Y
CMP [dp], Y
CMP sr, S
CMP (sr, S), Y
Cycle Penalties

See Also

External Links

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