User:HatZen08/draft

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Introduction

This is a list of the opcodes used in the 65816 processor. It is used by the Super Nintendo System (SNES) console.

For the registers, the following convention will be used:

Convention Description
A          the low byte of the accumulator, always 8-bit
B          the high byte of the accumulator, always 8-bit
C          the low and high bytes of the accumulator, always 16-bit
X          the X register, 8-bit or 16-bit
Y          the Y register, 8-bit or 16-bit
P          the processor register, always 8-bit

For the opcode arguments, the following convention will be used:

Argument   Example     Relative to
addr       LDA $1234   memory address, short, 16-bit
const      LDA #$80    constant, 8-bit or 16-bit
dp         LDA $10     direct page, relative, 8-bit
long       LDA $C21234 memory address, long, 24-bit
near       BRA $1234   branch, relative, 8-bit
sr         LDA $01,S   stack, relative, 8-bit

LDA, LDX, LDY

Reads a value from the memory and stores it in the specified register. LDA will store in the A or C register, LDX will store in the X register and LDY will store in the Y register.

flags
n highest bit of value loaded.
z set if data loaded is zero.
Opcode Syntax          Bytes   Notes
A9     LDA const       2       One extra byte if in 16-bit mode
AD     LDA addr        3
AF     LDA long        4
A5     LDA dp          2
B2     LDA (dp)        2
A7     LDA [dp]        2
BD     LDA addr,X      3
BF     LDA long,X      4
B9     LDA addr,Y      3
B5     LDA dp,X        2
A1     LDA (dp,X)      2
B1     LDA (dp),Y      2
B7     LDA [dp],Y      2
A3     LDA sr,S        2
B3     LDA (sr,S),Y    2
Opcode Syntax          Bytes   Notes
A2     LDX const       2       One extra byte if in 16-bit mode
AE     LDX addr        3
A6     LDX dp          2
BE     LDX addr,Y      3
B6     LDX dp,Y        2
Opcode Syntax          Bytes   Notes
A0     LDY const       2       One extra byte if in 16-bit mode
AC     LDY addr        3
A4     LDY dp          2
BC     LDY addr,X      3
B4     LDY dp,X        2

STA, STX, STY

Reads a value from the specified register and stores it in the memory. STA will read the A or C register, STX will read the X register and STY will read the Y register. All opcodes will store the retrieved value in the specified address.

The STZ opcode will always store the value of zero in the designed memory address. Unlike the STA, STX and STY opcodes, the STZ opcode doesn't affect flags. It also doesn't affect the A or C register.

flags
??

Opcode Syntax          Bytes   Notes
8D     STA addr        3
8F     STA long        4
85     STA dp          2
92     STA (dp)        2
87     STA [dp]        2
9D     STA addr,X      3
9F     STA long,X      4
99     STA addr,Y      3
95     STA dp,X        2
81     STA (dp,X)      2
91     STA (dp),Y      2
97     STA [dp],Y      2
83     STA sr,S        2
93     STA (sr,S),Y    2
Opcode Syntax          Bytes   Notes
8E     STX addr        3
86     STX dp          2
96     STX dp,Y        2
Opcode Syntax          Bytes   Notes
8C     STY addr        3
84     STY dp          2
94     STY dp,X        2  
Opcode Syntax          Bytes   Notes
9C     STZ addr        3
64     STZ dp          2
9E     STZ addr,X      3
74     STZ dp,X        2

TRB, TSB

Test all bits in the A or C register. For all bits set in the A or C register, the correspondent bits will be set or unset in the designed memory address. TSB will set the correspondent bits and TRB will reset the correspondent bits. All clear bits in the A or C register will be ignored and their correspondent bits in the designed address will not be altered.

flags
??
Opcode Syntax          Bytes   Notes
1C     TRB addr        3
14     TRB dp          2
Opcode Syntax          Bytes   Notes
0C     TSB addr        3
04     TSB dp          2

ADC, SBC

Add or subtract the value in the A or C register with the value in the designed memory address. ADC will add the value and SBC will subtract the value.

When the carry flag is set, a value of one will be added in the addition or subtraction operation.

The operation can overflow or underflow. It is the coder responsibility to check these cases and adjust the resulting value. A common method is to check the carry flag for overflow or underflow and cap the value to a prefixed setting.

flags:
n set if highest bit of result was set
v set if signed overflow?
z set if result is zero
c set if overflow or underflow
Opcode Syntax          Bytes   Notes
61     ADC (dp,X)      2
63     ADC sr,S        2
65     ADC dp          2
67     ADC [dp]        2
69     ADC const       2       One extra byte if in 16-bit mode
6D     ADC addr        3       
6F     ADC long        4
71     ADC (dp),Y      2
72     ADC (dp)        2
73     ADC (sr,S),Y    2
75     ADC dp,X        2
77     ADC [dp],Y      2
79     ADC addr,Y      3
7D     ADC addr,X      3
7F     ADC long,X      4
Opcode Syntax          Bytes   Notes
E9     SBC const       2       One extra byte if in 16-bit mode
ED     SBC addr        3
EF     SBC long        4
E5     SBC dp          2
F2     SBC (dp)        2
E7     SBC [dp]        2
FD     SBC addr,X      3
FF     SBC long,X      4
F9     SBC addr,Y      3
F5     SBC dp,X        2
E1     SBC (dp,X)      2
F1     SBC (dp),Y      2
F7     SBC [dp],Y      2
E3     SBC sr,S        2
F3     SBC (sr,S),Y    2

INC, INX, INY, DEC, DEX, DEY

Increment or decrement the specified register by one. It is equivalent to the ADC or SBC opcodes with the value of one without the carry flag set.

INC will increment the A or C register. INX will increment the X register. INY will increment the Y register. DEC will decrement the A or C register. DEX will decrement the X register. DEY will decrement the Y register. The operation can underflow or overflow.

flags:
n set if most significant bit of result is set.
z set if result is zero.
Opcode Syntax          Bytes   Notes
1A     INC             1       increment the A register
EE     INC addr        3
E6     INC dp          2
FE     INC addr,X      3
F6     INC dp,X        2
E8     INX             1       increment the X register
C8     INY             1       increment the Y register
Opcode Syntax          Bytes   Notes
3A     DEC             1       decrement register A
CE     DEC addr        3
C6     DEC dp          2
DE     DEC addr,X      3
D6     DEC dp,X        2
CA     DEX             1       decrement register X
88     DEY             1       decrement register Y

AND, ORA, EOR

A binary operation is done between the register A or C and the memory. The AND opcode will do a binary AND, the ORA opcode will do a binary OR and the EOR opcode will do a binary XOR. The result will be stored in the A or C register.

Flags:
n set if highest bit is set
z set if result is zero
Opcode Syntax          Bytes   Notes
21     AND (dp,X)      2
23     AND sr,S        2
25     AND dp          2
27     AND [dp]        2
29     AND const       2       One extra bit if in 16-bit mode
2D     AND addr        3
2F     AND long        4
31     AND (dp),Y      2
32     AND (dp)        2
33     AND (sr,S),Y    2
35     AND dp,X        2
37     AND [dp],Y      2
39     AND addr,Y      3
3D     AND addr,X      3
3F     AND long,X      4
Opcode Syntax          Bytes   Notes
09     ORA const       2       One extra byte if in 16-bit mode
0D     ORA addr        3
0F     ORA long        4
05     ORA dp          2
12     ORA (dp)        2
07     ORA [dp]        2
1D     ORA addr,X      3
1F     ORA long,X      4
19     ORA addr,Y      3
15     ORA dp,X        2
01     ORA (dp,X)      2
11     ORA (dp),Y      2
17     ORA [dp],Y      2
03     ORA sr,S        2
13     ORA (sr,S),Y    2
Opcode Syntax          Bytes   Notes
49     EOR const       2       One extra byte if in 16-bit mode
4D     EOR addr        3
4F     EOR long        4
45     EOR dp          2
52     EOR (dp)        2
47     EOR [dp]        2
5D     EOR addr,X      3
5F     EOR long,X      4
59     EOR addr,Y      3
55     EOR dp,X        2
41     EOR (dp,X)      2
51     EOR (dp),Y      2
57     EOR [dp],Y      2
43     EOR sr,S        2
53     EOR (sr,S),Y    2

BIT

Does a binary AND between the A or C register and the memory. Unlike the AND opcode, the binary AND operation only is done for the bits sets in the A or C register. All clear bits in the A or C register will be left clear after the operation.

flags:
n Takes value of most significant bit of memory data.
v Takes value from bit 6 or 14 of memory data.
z Set if logical AND of mem and acc is zero.
Opcode Syntax          Bytes   Notes
89     BIT const       2       Add one extra bit if in 16-bit mode
2C     BIT addr        3
24     BIT dp          2
3C     BIT addr,X      3
34     BIT dp,X        2

CMP, CPX, CPY

Compare the designed register with the memory and sets flags based on the comparison. CMP will compare the A or C register, CPX will compare the X register and CPY will compare the Y register. Generally, a conditional branch opcode, based on a flag status, is used after these opcodes.

flags:
n set if most significant bit of result is set
z set if result is zero
c set if register is equal or greater than memory

Opcode Syntax          Bytes   Notes
C9     CMP const       2       One extra byte if in 16-bit mode
CD     CMP addr        3
CF     CMP long        4
C5     CMP dp          2
D2     CMP (dp)        2
C7     CMP [dp]        2
DD     CMP addr,X      3
DF     CMP long,X      2
D9     CMP addr,Y      3
D5     CMP dp,X        2
C1     CMP (dp,X)      2
D1     CMP (dp),Y      2
D7     CMP [dp],Y      2
C3     CMP sr,S        2
D3     CMP (sr,S),Y    2
Opcode Syntax          Bytes   Notes
E0     CPX const       2       One extra byte if in 16-bit mode
EC     CPX addr        3
E4     CPX dp          2

Opcode Syntax          Bytes   Notes
C0     CPY const       2       One extra byte if in 16-bit mode
CC     CPY addr        3
C4     CPY dp          2

LSR, ASL

Shift bits in the designed register or memory address left or right. The LSR opcode will shift the bits right and the ASL opcode will shift the bits left.

LSR is equivalent to divide the number by two and ASL is equivalent to multiply the number by two. The operation can underflow or overflow. The bit shifted out will become the new carry. The bit shifted in is zero.

flags: LSR
n cleared.
z set if result is zero.
c bit zero becomes new carry.
flags: ASL
n set if most significant bit of result is set.
z set if result is zero.
c set if highest bit is moved into carry
Opcode Syntax          Bytes   Notes
4A     LSR             1       shift A register
4E     LSR addr        3
46     LSR dp          2
5E     LSR addr,X      3
56     LSR dp,X        2
Opcode Syntax          Bytes   Notes
06     ASL dp          2
0A     ASL             1       The operand is the register A
0E     ASL addr        3
16     ASL dp,X        2
1E     ASL addr,X      3

ROL, ROR

Shift bits in the designed register or memory address left or right. The ROL opcode will shift the bits left and the ROR opcode will shift the bits right.

The bit shifted in is the old carry. The bit shifted out will be the new carry.

flags: ROL
n set if most significant bit of result is set.
z set if result is zero.
c the high bit (7 or 15) becomes the new carry.
flags: ROR
n set if most significant bit of result is set.
z set if result is zero.
c low bit becomes the new carry.
Opcode Syntax          Bytes   Notes
2A     ROL             1       affects register A
2E     ROL addr        3
26     ROL dp          2
3E     ROL addr,X      3
36     ROL dp,X        2
Opcode Syntax          Bytes   Notes
6A     ROR             1       affects A register
6E     ROR addr        3
66     ROR dp          2
7E     ROR addr,X      3
76     ROR dp,X        2

BPL, BMI, BRA, BCC, BCS, BNE, BEQ, BVC, BVS, BRL

Change the execution flow based on a conditional branch. If the condition is meet, the execution flow will be changed for the designed address. Otherwise, it continues normally.

The majority of the conditional branches are based in flag status. The flags were setup by anterior opcodes.

flags:
none
Opcode Syntax          Bytes   Notes
10     BPL near        2       BPL - branch if minus flag is clear, branch if plus
30     BMI near        2       BMI - branch if minus flag set, branch if minus
80     BRA near        2       BRA - always branch
90     BCC near        2       BCC - branch if carry flag clear
B0     BCS near        2       BCS - branch if carry flag set 
D0     BNE near        2       BNE - branch if zero flag clear, branch if not equal
F0     BEQ near        2       BEQ - branch if zero flag set, branch if equal
50     BVC near        2       BVC - branch if overflow clear
70     BVS near        2       BVS - branch if overflow set
82     BRL addr        3       similar to BRA, but with longer range

JMP

Change the execution flow to the designed address.

flags:
none
Opcode Syntax          Bytes   Notes
4C     JMP addr        3
6C     JMP (addr)      3
7C     JMP (addr,X)    3
5C     JMP long        4
DC     JMP [addr]      3

JSR, JSL

Calls a sub routine which will be executed.

The JSR opcode will put two bytes in the stack, relative to the return address. It is expected that they will be retrieved by an RTS opcode in the sub routine.

The JSL opcode will put three bytes in the stack, relative to the return address. It is expected that they will be retrieved by an RTL opcode in the sub routine.

Opcode Syntax          Bytes   Notes
22     JSL long        4
20     JSR addr        3
FC     JSR (addr,X)    3 

RTS, RTL

RTS will pull two bytes from the stack and RTL will pull three bytes from the stack. They will be setup as the new control flow address.

It is expected that the bytes in the stack were pushed from a JSR opcode for the RTS opcode and from a JSL opcode for the RTL opcode.

flags:
none
Opcode Syntax          Bytes   Notes
6B     RTL             1       pull three bytes from the stack as the return address
60     RTS             1       pull two bytes from the stack as the return address

CLC, CLD, CLI, CLV, SEC, SED, SEI

Set or reset flags.

Opcode Syntax          Bytes   Notes
18     CLC             1       clear carry flag
D8     CLD             1       clear decimal flag
58     CLI             1       clear interrupt flag 
B8     CLV             1       clear overflow flag
38     SEC             1       set carry flag
F8     SED             1       set decimal flag
78     SEI             1       set interrupt flag

TAX, TAY, TXA, TYA, TSX, TXS, TXY, TYX, TCD, TDC, TCS, TSC

Transfer bytes between the specified registers or special addresses.

If the setting of the registers have different settings of 8-bit or 16-bit, the copy of B can be truncated based on the opcode behavior. It is possible that a leftover value of B will be left untouched in the B register.

flags: all except TCS
n set if most significant bit of transfer value is set.
z set if transferred value is zero.
Opcode Syntax          Bytes   Notes
AA     TAX             1       from A or C to X register
A8     TAY             1       from A or C to Y register
8A     TXA             1       from X register to A or C
98     TYA             1       from Y register to A or C
BA     TSX             1       from stack pointer to X register
9A     TXS             1       from X register to stack pointer
9B     TXY             1       from X register to Y register
BB     TYX             1       from Y register to X register
5B     TCD             1       from C to direct page
7B     TDC             1       from direct page to C 
1B     TCS             1       from C to stack pointer
3B     TSC             1       from stack pointer to C

MVP, MVN

Move a block of bytes from a specified address to another address. The X register will be the start address to copy from. The Y register will be start address to copy to. The C register will be the number of bytes to copy minus one.

The opcode arguments are the source bank and the destination bank, in this order.

MVP must be used if the Y register is greater than the X register. Otherwise, MVN must be used instead.

Opcode Syntax          Bytes   Notes
54     MVN src,dest    3
44     MVP src,dest    3

PEA, PEI, PER

Push bytes in the stack, based on the opcodes arguments. They always work in 16-bit mode.

Opcode Syntax          Bytes   Notes
F4     PEA const       3       the argument is always 16-bit
D4     PEI (dp)        2 
62     PER label       3

PHA, PHP, PHX, PHY, PHB, PHD, PHK, PLA, PLP, PLX, PLY, PLB, PLD

Push or pull bytes from the stack. The setting of the register or special address as 8-bit or 16-bit will set the number of bytes pushed/pulled from the stack.

flags: PHA/PHP/PHX/PHY/PHB/PHD/PHK
none
flags: PLA/PLX/PLY/PLB/PLD
n set if most significant bit of result is set.
z set if result is zero.
Opcode Syntax          Bytes   Notes
48     PHA             1       push A or C register
08     PHP             1       push flag register (8-bit)
DA     PHX             1       push X register (8-bit or 16-bit)
5A     PHY             1       push Y register (8-bit or 16-bit)
8B     PHB             1       push data bank register (8-bit)
0B     PHD             1       push direct page register (16-bit)
4B     PHK             1       push program bank register (8-bit)
Opcode Syntax          Bytes   Notes
68     PLA             1       pull A or C register
28     PLP             1       pull flag register (8-bit)(sets all flags)
FA     PLX             1       pull X register (8-bit or 16-bit)
7A     PLY             1       pull Y register (8-bit or 16-bit)
AB     PLB             1       pull pull data bank register (8-bit)
2B     PLD             1       pull direct page register (16-bit)             

NOP

Does absolutely nothing. It is mostly used to waste cycles. A few special registers or addresses can't be fetch until a minimum number of cycles has passed.

If the coder needs to erase a code segment, a conditional branch or jump is recommended instead of a long line of NOP opcodes.

Opcode Syntax          Bytes   Notes
EA     NOP             1 

REP, SEP

Setups the processor flags with the opcode arguments. For each bit set in the argument, the correspondent flag is set or reset. REP will reset the flags and SEP will set the flags.

arguments:
#$01 carry flag
#$02 zero flag
#$04 irq flag?
#$08 decimal mode
#$10 X and Y register: 0 = 16-bit, 1 = 8-bit
#$20 accumulator: 0 = 16-bit, 1 = 8-bit
#$40 overflow flag
#$80 negative flag
flags:
all
Opcode Syntax          Bytes   Notes
C2     REP const       2       const is always 8-bit
E2     SEP const       2       const is always 8-bit

XBA

Exchanges the A and B registers.

flags:
n Set if the most significant bit of the new value in the low order 8 bits (A) of the accumulator is set. (former bit 15)
z Set if new value of the lower order 8 bit accumulator (A) is zero.
Opcode Syntax          Bytes   Notes
EB     XBA             1

XCE

Exchanges the carry flag and the emulation flag.

flags:
e from previous carry flag.
c from previous emulation flag.
m native mode flag only. switching to native 65816 mode sets to one.
x x is a native mode flag only.
b brk is an emulation 6502 flag only. it is set to 1 to become the x flag in native mode
Opcode Syntax          Bytes   Notes
FB     XCE             1

Miscellaneous

Opcode Syntax          Bytes   Notes
00     BRK             ??      software break
02     COP const       ??      coprocessor empowerment
40     RTI             1       return from interrupt
DB     STP             1       stop processor
CB     WAI             1       wait for interrupt