Address Modes

• A accumulator OPC A operand is AC (implied single byte instruction)
• abs absolute OPC $LLHH operand is address $HHLL *
• abs,X absolute, X-indexed OPC $LLHH,X operand is address; effective address is address incremented by X with carry **
• abs,Y absolute, Y-indexed OPC $LLHH,Y operand is address; effective address is address incremented by Y with carry **
• # immediate OPC #$BB operand is byte BB
• impl implied OPC operand implied
• ind indirect OPC ($LLHH) operand is address; effective address is contents of word at address: C.w($HHLL)
• X,ind X-indexed, indirect OPC ($LL,X) operand is zeropage address; effective address is word in (LL + X, LL + X + 1), inc. without carry: C.w($00LL + X)
• ind,Y indirect, Y-indexed OPC ($LL),Y operand is zeropage address; effective address is word in (LL, LL + 1) incremented by Y with carry: C.w($00LL) + Y
• rel relative OPC $BB branch target is PC + signed offset BB ***
• zpg zeropage OPC $LL operand is zeropage address (hi-byte is zero, address = $00LL)
• zpg,X zeropage, X-indexed OPC $LL,X operand is zeropage address; effective address is address incremented by X without carry **
• zpg,Y zeropage, Y-indexed OPC $LL,Y operand is zeropage address; effective address is address incremented by Y without carry **

* 16-bit address words are little endian, lo(w)-byte first, followed by the hi(gh)-byte. An assembler will use a human readable, big-endian notation as in $HHLL.

** The available 16-bit address space is conceived as consisting of pages of 256 bytes each, with address hi-bytes represententing the page index. An increment with carry may affect the hi-byte and may thus result in a crossing of page boundaries, adding an extra cycle to the execution. Increments without carry do not affect the hi-byte of an address and no page transitions do occur. Generally, increments of 16-bit addresses include a carry, increments of zeropage addresses don't. Notably this is not related in any way to the state of the carry bit of the accumulator.

*** Branch offsets are signed 8-bit values, -128 ... +127, negative offsets in two's complement. Page transitions may occur and add an extra cycle to the exucution.

Registers

• PC program counter (16 bit)
• AC accumulator (8 bit)
• X X register (8 bit)
• Y Y register (8 bit)
• SR status register NV-BDIZC (8 bit)
• SP stack pointer (8 bit)

SR Flags NV-BDIZC

bit 7 to bit 0

N ....  Negative
V ....  Overflow
- ....  ignored
B ....  Break
D ....  Decimal (use BCD for arithmetics)
I ....  Interrupt (IRQ disable)
Z ....  Zero
C ....  Carry

Processor Stack

LIFO, top down, 8 bit range 0x0100 - 0x01FF

Bytes, Words, Addressing

8 bit bytes, 16 bit words in lobyte-hibyte representation (Little-Endian). 16 bit address range, operands follow instruction codes.

Signed values are two's complement, sign in bit 7 (most significant bit).

• %11111111 = $FF = -1
• %10000000 = $80 = -128
• %01111111 = $7F = +127

Standard 6502 opcodes

K65 compiler supports following 6502 instructions. TBD value means that instruction support is planned, but currently not implemented.

ADC AND ASL BCC BCS BEQ BIT BMI BNE BPL BRK BVC BVS CLC CLD CLI CLV CMP CPX CPY DEC DEX DEY EOR INC INX INY JMP JSR LDA LDX LDY LSR NOP ORA PHA PHP PLA PLP ROL ROR RTI RTS SBC SEC SED SEI STA STX STY TAX TAY TSX TXA TXS TYA

---

ADC add with carry

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a+imm	a+mem	a+mem,x	a+mem,y	a+(mem,x)	a+(mem),y

ADC  Add Memory to Accumulator with Carry

     A + M + C -> A, C                N Z C I D V
                                      + + + - - +

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     ADC #oper     69    2     2
     zeropage      ADC oper      65    2     3
     zeropage,X    ADC oper,X    75    2     4
     absolute      ADC oper      6D    3     4
     absolute,X    ADC oper,X    7D    3     4*
     absolute,Y    ADC oper,Y    79    3     4*
     (indirect,X)  ADC (oper,X)  61    2     6
     (indirect),Y  ADC (oper),Y  71    2     5*

---

AND and (with accumulator)

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a&imm	a&mem	a&mem,x	a&mem,y	a&(mem,x)	a&(mem),y

AND  AND Memory with Accumulator

     A AND M -> A                     N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     AND #oper     29    2     2
     zeropage      AND oper      25    2     3
     zeropage,X    AND oper,X    35    2     4
     absolute      AND oper      2D    3     4
     absolute,X    AND oper,X    3D    3     4*
     absolute,Y    AND oper,Y    39    3     4*
     (indirect,X)  AND (oper,X)  21    2     6
     (indirect),Y  AND (oper),Y  31    2     5*

---

ASL arithmetic shift left

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
a<<			mem<<	mem,x<<

ASL  Shift Left One Bit (Memory or Accumulator)

     C <- [76543210] <- 0             N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     accumulator   ASL A         0A    1     2
     zeropage      ASL oper      06    2     5
     zeropage,X    ASL oper,X    16    2     6
     absolute      ASL oper      0E    3     6
     absolute,X    ASL oper,X    1E    3     7

---

BCC branch on carry clear

• >={ ... }
• < goto label
• { ... } <
• c+?{ ... }
• c-? goto label
• { ... } c-?

BCC  Branch on Carry Clear

     branch on C = 0                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BCC oper      90    2     2**

---

BCS branch on carry set

• <{ ... }
• >= goto label
• { ... } >=
• c-?{ ... }
• c+? goto label
• { ... } c+?

BCS  Branch on Carry Set

     branch on C = 1                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BCS oper      B0    2     2**

---

BEQ branch on equal (zero set)

• !={ ... }
• == goto label
• { ... } ==
• z-?{ ... }
• z+? goto label
• { ... } z+?

BEQ  Branch on Result Zero

     branch on Z = 1                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BEQ oper      F0    2     2**

---

BIT bit test

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			a&?mem

BIT  Test Bits in Memory with Accumulator

     bits 7 and 6 of operand are transfered to bit 7 and 6 of SR (N,V);
     the zeroflag is set to the result of operand AND accumulator.

     A AND M, M7 -> N, M6 -> V        N Z C I D V
                                     M7 + - - - M6

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      BIT oper      24    2     3
     absolute      BIT oper      2C    3     4

---

BMI branch on minus (negative set)

• >=0{ ... }
• <0 goto label
• { ... } <0
• n-?{ ... }
• n+? goto label
• { ... } n+?

BMI  Branch on Result Minus

     branch on N = 1                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BMI oper      30    2     2**

---

BNE branch on not equal (zero clear)

• =={ ... }
• != goto label
• { ... } !=
• z+?{ ... }
• z-? goto label
• { ... } z-?

BNE  Branch on Result not Zero

     branch on Z = 0                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BNE oper      D0    2     2**

---

BPL branch on plus (negative clear)

• <0{ ... }
• >=0 goto label
• { ... } >=0
• n+?{ ... }
• n-? goto label
• { ... } n-?

BPL  Branch on Result Plus

     branch on N = 0                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BPL oper      10    2     2**

---

BRK interrupt

/* TBD */

BRK  Force Break

     interrupt,                       N Z C I D V
     push PC+2, push SR               - - - 1 - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       BRK           00    1     7

---

BVC branch on overflow clear

• <<={ ... }
• >>= goto label
• { ... } >>=
• v+{ ... }
• v- goto label
• { ... } v-

BVC  Branch on Overflow Clear

     branch on V = 0                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BVC oper      50    2     2**

---

BVS branch on overflow set

• >>={ ... }
• <<= goto label
• { ... } <<=
• v-{ ... }
• v+ goto label
• { ... } v+

BVS  Branch on Overflow Set

     branch on V = 1                  N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     relative      BVC oper      70    2     2**

---

CLC clear carry

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	c-

CLC  Clear Carry Flag

     0 -> C                           N Z C I D V
                                      - - 0 - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       CLC           18    1     2

---

CLD clear decimal

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	d-

CLD  Clear Decimal Mode

     0 -> D                           N Z C I D V
                                      - - - - 0 -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       CLD           D8    1     2

---

CLI clear interrupt disable

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	i-

CLI  Clear Interrupt Disable Bit

     0 -> I                           N Z C I D V
                                      - - - 0 - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       CLI           58    1     2

---

CLV clear overflow

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	o-

CLV  Clear Overflow Flag

     0 -> V                           N Z C I D V
                                      - - - - - 0

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       CLV           B8    1     2

---

CMP compare (with accumulator)

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a?imm	a?mem	a?mem,x	a?mem,y	a?(mem,x)	a?(mem),y

CMP  Compare Memory with Accumulator

     A - M                            N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     CMP #oper     C9    2     2
     zeropage      CMP oper      C5    2     3
     zeropage,X    CMP oper,X    D5    2     4
     absolute      CMP oper      CD    3     4
     absolute,X    CMP oper,X    DD    3     4*
     absolute,Y    CMP oper,Y    D9    3     4*
     (indirect,X)  CMP (oper,X)  C1    2     6
     (indirect),Y  CMP (oper),Y  D1    2     5*

---

CPX compare with X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		x?imm	x?mem

CPX  Compare Memory and Index X

     X - M                            N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     CPX #oper     E0    2     2
     zeropage      CPX oper      E4    2     3
     absolute      CPX oper      EC    3     4

---

CPY compare with Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		y?imm	y?mem

CPY  Compare Memory and Index Y

     Y - M                            N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     CPY #oper     C0    2     2
     zeropage      CPY oper      C4    2     3
     absolute      CPY oper      CC    3     4

---

DEC decrement

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			mem--	mem,x--

DEC  Decrement Memory by One

     M - 1 -> M                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      DEC oper      C6    2     5
     zeropage,X    DEC oper,X    D6    2     6
     absolute      DEC oper      CE    3     6
     absolute,X    DEC oper,X    DE    3     7

---

DEX decrement X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	x--

DEX  Decrement Index X by One

     X - 1 -> X                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       DEC           CA    1     2

---

DEY decrement Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	y--

DEY  Decrement Index Y by One

     Y - 1 -> Y                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       DEC           88    1     2

---

EOR exclusive or (with accumulator)

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a^imm	a^mem	a^mem,x	a^mem,y	a^(mem,x)	a^(mem),y

EOR  Exclusive-OR Memory with Accumulator

     A EOR M -> A                     N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     EOR #oper     49    2     2
     zeropage      EOR oper      45    2     3
     zeropage,X    EOR oper,X    55    2     4
     absolute      EOR oper      4D    3     4
     absolute,X    EOR oper,X    5D    3     4*
     absolute,Y    EOR oper,Y    59    3     4*
     (indirect,X)  EOR (oper,X)  41    2     6
     (indirect),Y  EOR (oper),Y  51    2     5*

---

INC increment

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			mem++	mem,x++

INC  Increment Memory by One

     M + 1 -> M                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      INC oper      E6    2     5
     zeropage,X    INC oper,X    F6    2     6
     absolute      INC oper      EE    3     6
     absolute,X    INC oper,X    FE    3     7

---

INX increment X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	x++

INX  Increment Index X by One

     X + 1 -> X                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       INX           E8    1     2

---

INY increment Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	y++

INY  Increment Index Y by One

     Y + 1 -> Y                       N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       INY           C8    1     2

---

JMP jump

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			goto mem					goto (mem)

JMP  Jump to New Location

     (PC+1) -> PCL                    N Z C I D V
     (PC+2) -> PCH                    - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     absolute      JMP oper      4C    3     3
     indirect      JMP (oper)    6C    3     5

---

JSR jump subroutine

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			call mem

JSR  Jump to New Location Saving Return Address

     push (PC+2),                     N Z C I D V
     (PC+1) -> PCL                    - - - - - -
     (PC+2) -> PCH

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     absolute      JSR oper      20    3     6

---

LDA load accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a=imm	a=mem	a=mem,x	a=mem,y	a=(mem,x)	a=(mem),y

LDA  Load Accumulator with Memory

     M -> A                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     LDA #oper     A9    2     2
     zeropage      LDA oper      A5    2     3
     zeropage,X    LDA oper,X    B5    2     4
     absolute      LDA oper      AD    3     4
     absolute,X    LDA oper,X    BD    3     4*
     absolute,Y    LDA oper,Y    B9    3     4*
     (indirect,X)  LDA (oper,X)  A1    2     6
     (indirect),Y  LDA (oper),Y  B1    2     5*

---

LDX load X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		x=imm	x=mem		x=mem,y

LDX  Load Index X with Memory

     M -> X                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     LDX #oper     A2    2     2
     zeropage      LDX oper      A6    2     3
     zeropage,Y    LDX oper,Y    B6    2     4
     absolute      LDX oper      AE    3     4
     absolute,Y    LDX oper,Y    BE    3     4*

---

LDY load Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		y=imm	y=mem	y=mem,x

LDY  Load Index Y with Memory

     M -> Y                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     LDY #oper     A0    2     2
     zeropage      LDY oper      A4    2     3
     zeropage,X    LDY oper,X    B4    2     4
     absolute      LDY oper      AC    3     4
     absolute,X    LDY oper,X    BC    3     4*

---

LSR logical shift right

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
a>>			mem>>	mem,x>>

LSR  Shift One Bit Right (Memory or Accumulator)

     0 -> [76543210] -> C             N Z C I D V
                                      0 + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     accumulator   LSR A         4A    1     2
     zeropage      LSR oper      46    2     5
     zeropage,X    LSR oper,X    56    2     6
     absolute      LSR oper      4E    3     6
     absolute,X    LSR oper,X    5E    3     7

---

NOP no operation

• * for single NOP
• *<number> to wait <number> of cycles.

Even values generate the number of NOP instructions equal to number / 2. Odd values generate (number - 1) / 2 + one illegal instruction NOP #0 3 cycles long.

NOP  No Operation

     ---                              N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       NOP           EA    1     2

---

ORA or with accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a|imm	a|mem	a|mem,x	a|mem,y	a|(mem,x)	a|(mem),y

ORA  OR Memory with Accumulator

     A OR M -> A                      N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     ORA #oper     09    2     2
     zeropage      ORA oper      05    2     3
     zeropage,X    ORA oper,X    15    2     4
     absolute      ORA oper      0D    3     4
     absolute,X    ORA oper,X    1D    3     4*
     absolute,Y    ORA oper,Y    19    3     4*
     (indirect,X)  ORA (oper,X)  01    2     6
     (indirect),Y  ORA (oper),Y  11    2     5*

---

PHA push accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	a!!

PHA  Push Accumulator on Stack

     push A                           N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       PHA           48    1     3

---

PHP push processor status (SR)

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	flag!!

PHP  Push Processor Status on Stack

     push SR                          N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       PHP           08    1     3

---

PLA pull accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	a??

PLA  Pull Accumulator from Stack

     pull A                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       PLA           68    1     4

---

PLP pull processor status (SR)

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	flag??

PLP  Pull Processor Status from Stack

     pull SR                          N Z C I D V
                                      from stack

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       PLP           28    1     4

---

ROL rotate left

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
a<<<		mem<<<	mem,x<<<

ROL  Rotate One Bit Left (Memory or Accumulator)

     C <- [76543210] <- C             N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     accumulator   ROL A         2A    1     2
     zeropage      ROL oper      26    2     5
     zeropage,X    ROL oper,X    36    2     6
     absolute      ROL oper      2E    3     6
     absolute,X    ROL oper,X    3E    3     7

---

ROR rotate right

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
a>>>		mem>>>	mem,x>>>

ROR  Rotate One Bit Right (Memory or Accumulator)

     C -> [76543210] -> C             N Z C I D V
                                      + + + - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     accumulator   ROR A         6A    1     2
     zeropage      ROR oper      66    2     5
     zeropage,X    ROR oper,X    76    2     6
     absolute      ROR oper      6E    3     6
     absolute,X    ROR oper,X    7E    3     7

---

RTI return from interrupt

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	return_i

RTI  Return from Interrupt

     pull SR, pull PC                 N Z C I D V
                                      from stack

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       RTI           40    1     6

---

RTS return from subroutine

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	return

RTS  Return from Subroutine

     pull PC, PC+1 -> PC              N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       RTS           60    1     6

---

SBC subtract with carry

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
		a-imm	a-mem	a-mem,x	a-mem,y	a-(mem,x)	a-(mem),y

SBC  Subtract Memory from Accumulator with Borrow

     A - M - C -> A                   N Z C I D V
                                      + + + - - +

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     immidiate     SBC #oper     E9    2     2
     zeropage      SBC oper      E5    2     3
     zeropage,X    SBC oper,X    F5    2     4
     absolute      SBC oper      ED    3     4
     absolute,X    SBC oper,X    FD    3     4*
     absolute,Y    SBC oper,Y    F9    3     4*
     (indirect,X)  SBC (oper,X)  E1    2     6
     (indirect),Y  SBC (oper),Y  F1    2     5*

---

SEC set carry

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	c+

SEC  Set Carry Flag

     1 -> C                           N Z C I D V
                                      - - 1 - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       SEC           38    1     2

---

SED set decimal

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	d+

SED  Set Decimal Flag

     1 -> D                           N Z C I D V
                                      - - - - 1 -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       SED           F8    1     2

---

SEI set interrupt disable

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	i+

SEI  Set Interrupt Disable Status

     1 -> I                           N Z C I D V
                                      - - - 1 - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       SEI           78    1     2

---

STA store accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			mem=a	mem,x=a	mem,y=a	(mem,x)=a	(mem),y=a

STA  Store Accumulator in Memory

     A -> M                           N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      STA oper      85    2     3
     zeropage,X    STA oper,X    95    2     4
     absolute      STA oper      8D    3     4
     absolute,X    STA oper,X    9D    3     5
     absolute,Y    STA oper,Y    99    3     5
     (indirect,X)  STA (oper,X)  81    2     6
     (indirect),Y  STA (oper),Y  91    2     6

---

STX store X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			mem=x

STX  Store Index X in Memory

     X -> M                           N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      STX oper      86    2     3
     zeropage,Y    STX oper,Y    96    2     4
     absolute      STX oper      8E    3     4

---

STY store Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
			mem=y

STY  Sore Index Y in Memory

     Y -> M                           N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     zeropage      STY oper      84    2     3
     zeropage,X    STY oper,X    94    2     4
     absolute      STY oper      8C    3     4

---

TAX transfer accumulator to X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	x=a

TAX  Transfer Accumulator to Index X

     A -> X                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TAX           AA    1     2

---

TAY transfer accumulator to Y

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	y=a

TAY  Transfer Accumulator to Index Y

     A -> Y                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TAY           A8    1     2

---

TSX transfer stack pointer to X

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	x=s

TSX  Transfer Stack Pointer to Index X

     SP -> X                          N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TSX           BA    1     2

---

TXA transfer X to accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	a=x

TXA  Transfer Index X to Accumulator

     X -> A                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TXA           8A    1     2

---

TXS transfer X to stack pointer

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	s=x

TXS  Transfer Index X to Stack Register

     X -> SP                          N Z C I D V
                                      - - - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TXS           9A    1     2

---

TYA transfer Y to accumulator

Acc	Implied	Imm	Mem	Mem,X	Mem,Y	(Mem,X)	(Mem),Y	(Mem)
	a=y

TYA  Transfer Index Y to Accumulator

     Y -> A                           N Z C I D V
                                      + + - - - -

     addressing    assembler    opc  bytes  cyles
     --------------------------------------------
     implied       TYA           98    1     2

---

Note

* add 1 to cycles if page boundery is crossed

** add 1 to cycles if branch occurs on same page add 2 to cycles if branch occurs to different page

Legend to Flags

 + .... modified
 - .... not modified
 1 .... set
 0 .... cleared
M6 .... memory bit 6
M7 .... memory bit 7