The following instruction set shows the ideal operations to be supported by Juno and is used to assess the various designs.
Load / Store Operations
Instruction
|
Address mode
|
Description
|
Example
|
Code
|
Length
|
Flags
|
LDA
|
Immediate
|
Load A with
the value given in the operand
|
LDA #44
|
1
|
2
|
N, Z
|
LDA
|
Absolute
|
Load A with the value at the
address specified in the operand
|
LDA &0x100
|
2
|
3
|
N, Z
|
LDA
|
Absolute with
index register
|
Load A with
the value at the address calculated by adding the index register to the
address given in the operand.
|
LDA
&0x100,x
|
3
|
3
|
N, Z
|
LDA
|
Memory indirect
|
Load A with the value at the
address pointed to by the address given in the operand.
|
LDA (&0x100)
|
4
|
3
|
N,Z
|
STA
|
Absolute
|
Store the
value of A at the address specified in the operand
|
STA
&0x100
|
5
|
3
|
tbc
|
STA
|
Absolute with index register
|
Store the value of A at the
address calculated by adding the index register to the address given in the
operand.
|
STA &0x100,x
|
6
|
3
|
tbc
|
STA
|
Memory
indirect
|
Store the
value of A at the address pointed to by the address given in the operand.
|
STA
(&0x100)
|
7
|
3
|
tbc
|
LDX
|
Immediate
|
Load X with the value given in the
operand
|
LDX #22
|
8
|
2
|
N, Z
|
LDX
|
Absolute
|
Load X with
the value at the address in the operand
|
LDX
&0x200
|
9
|
3
|
N,Z
|
STX
|
Absolute
|
Store the value of X at the
address specified in the operand
|
STX &0x200
|
10
|
3
|
tbc
|
Arithmetic Group
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
ADD
|
Immediate
|
Add the value
given in the operand to A. Ignore carry.
|
ADD #12
|
11
|
2
|
N, V, Z, C
|
ADD
|
Absolute
|
Add the value at the address
specified in the operand to A. Ignore carry.
|
ADD &0x100
|
12
|
3
|
N, V, Z, C
|
ADC
|
Immediate
|
Add the value
given in the operand to A with carry.
|
ADC #12
|
13
|
2
|
N, V, Z, C
|
ADC
|
Absolute
|
Add the value at the address
specified in the operand to A with carry.
|
ADC &0x100
|
14
|
3
|
N, V, Z, C
|
SUB
|
Immediate
|
Subtract the
value specified in the operand from A. Ignore carry
|
SUB #12
|
15
|
2
|
N, V, Z, C
|
SUB
|
Absolute
|
Subtract the value at the address
specified in the operand from A. Ignore carry
|
SUB &0x100
|
16
|
3
|
N, V, Z, C
|
SBC
|
Immediate
|
Subtract the
value specified in the operand from with carry.
|
SBC #12
|
17
|
2
|
N, V, Z, C
|
SBC
|
Absolute
|
Subtract the value at the address
specified in the operand from A with carry.
|
SBC &0x100
|
18
|
3
|
N, V, Z, C
|
CMP
|
Immediate
|
Compare the
value specified in the operand with A by subtracting the value from A to set
the flags but not storing the result in A.
|
CMP #12
|
19
|
2
|
N, Z, C
|
CMP
|
Absolute
|
Compare the value at the address
specified in the operand with A.
|
CMP &0x100
|
20
|
3
|
N, Z, C
|
CPX
|
Immediate
|
Compare the
value specified in the operand with X by subtracting the value from X to set
the flags but not storing the result in X.
|
CPX #12
|
21
|
2
|
N, Z, C
|
CPX
|
Absolute
|
Compare the value at the address
specified in the operand with X.
|
CPX &0x100
|
22
|
3
|
N, Z, C
|
DEX
|
Implied
|
Decrement X
by 1
|
DEX
|
23
|
1
|
N, V, Z, C
|
INX
|
Implied
|
Increment X by 1
|
INX
|
24
|
1
|
N, V, Z, C
|
ADS
|
Immediate
|
Increment
Stack Pointer by the value in the operand. Used to support passing parameters
to subroutines via the stack
|
INS #4
|
25
|
2
|
N, V, Z, C
|
SUS
|
Immediate
|
Decrement Stack Pointer by the
value in the operand. Used to support passing parameters to subroutines via
the stack
|
SUS #4
|
26
|
2
|
N, V, Z, C
|
Logical Group
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
AND
|
Immediate
|
Logical AND
the value in the operand with A
|
AND #22
|
27
|
2
|
N, Z
|
AND
|
Absolute
|
Logical AND the value at the
address specified in the operand with A
|
AND &0x100
|
28
|
3
|
N, Z
|
OR
|
Immediate
|
Logical
inclusive OR the value in the operand with A
|
OR #22
|
29
|
2
|
N, Z
|
OR
|
Absolute
|
Logical inclusive OR the value at
the address specified in the operand with A
|
OR &0x100
|
30
|
3
|
N, Z
|
XOR
|
Immediate
|
Logical
exclusive OR the value in the operand with A
|
XOR #22
|
31
|
2
|
N, Z
|
XOR
|
Absolute
|
Logical exclusive OR the value at
the address specified in the operand with A
|
XOR &0x100
|
32
|
3
|
N, Z
|
BIT
|
Immediate
|
Test bits by
performing a logical AND with the value in the operand and A to set the flags
and disregard the result
|
BIT #22
|
33
|
2
|
N, Z
|
Branch Group
Branches are
relative jumps and can cause a branch based on testing a flag to an address
that is in the range +127 to -128 of the current instruction. Code that only
uses branches is relocatable.
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
BCC
|
Absolute
|
Branch on
Carry Clear (C=0)
|
BCC #10
|
34
|
2
|
n/a
|
BCS
|
Absolute
|
Branch on Carry Set (C=1)
|
BCS #246
|
35
|
2
|
n/a
|
BEQ
|
Absolute
|
Branch on
Equal to zero (Z=1)
|
BEQ .label
|
36
|
2
|
n/a
|
BNE
|
Absolute
|
Branch on Not Equal to zero (Z=1)
|
BNE .label
|
37
|
2
|
n/a
|
BMI
|
Absolute
|
Branch on
MInus (N=1)
|
BMI .label
|
38
|
2
|
n/a
|
BPL
|
Absolute
|
Branch on Plus (N=0)
|
BPL .label
|
39
|
2
|
n/a
|
BVC
|
Absolute
|
Branch on
oVerflow Clear (V=0)
|
BVC .label
|
40
|
2
|
n/a
|
BVS
|
Absolute
|
Branch on oVerflow Set (V=1)
|
BVS .label
|
41
|
2
|
n/a
|
Jump & Calls Group
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
JMP
|
Absolute
|
Jump to the
address specified by the operand
|
JMP &0x100
|
42
|
3
|
n/a
|
JMP
|
Memory Indirect
|
Jump to the address pointed to by
the address given in the operand.
|
JMP (&0x100)
|
43
|
3
|
n/a
|
JSR
|
Absolute
|
Pushes the
address of the next instruction onto the stack and jumps to the address
specified by the operand
|
JSR
&0x100
|
44
|
3
|
n/a
|
RTS
|
Implied
|
Pops the address from the stack
and transfers control to that address
|
RTS
|
45
|
1
|
n/a
|
Stack Group
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
PHA
|
Implied
|
Push A onto
the stack
|
PHA
|
46
|
1
|
n/a
|
PHX
|
Implied
|
Push X onto the stack
|
PHX
|
47
|
1
|
n/a
|
PHP
|
Implied
|
Push
Processor status register onto the stack
|
PHP
|
48
|
1
|
n/a
|
PLA
|
Implied
|
Pop A from the stack
|
PLA
|
49
|
1
|
N, Z
|
PLX
|
Implied
|
Pop X from
the stack
|
PLX
|
50
|
1
|
N, Z
|
PLP
|
Implied
|
Pop Process status register from
the stack
|
PLP
|
51
|
1
|
N, Z
|
Control Group
Instruction
|
Address mode
|
Example
|
Code
|
Bytes
|
Flags
|
|
NOP
|
Implied
|
Do nothing
|
NOP
|
0
|
1
|
n/a
|
CLC
|
Implied
|
Clear Carry flag
|
CLC
|
52
|
1
|
C
|
CLV
|
Implied
|
Clear
oVerflow flag
|
CLV
|
53
|
1
|
V
|
Notes:
i) Notation
-
#b Absolute
value. One byte in size.
-
&bb Address.
An Address is two bytes
-
(&bb) Indirect
-
0x Hexadecimal
-
0b Binary
-
. Label.
At the start of the line defines a label. Otherwise a reference
-
ii) Other types of instruction not included in v1 of the
instruction set
a.
Rotate and shift
b.
Interrupt related instructions
iii) For reference an overview of Addressing modes
Immediate
|
The data is
stored as part of the instruction e.g. LDA #44
|
Implicit
|
The address is implied by the
instruction and does not need to be stated as part of the instruction e.g.
POP
|
Absolute
|
The effective
address is part of the instruction e.g. LDA (0x100)
|
Absolute with index register
|
The
effective address is the calculated by adding the index register value to the
absolute address
|
Register direct
|
The source and/or destination is a register e.g. MOV R0,R1
|
Register indirect
|
The
contents of the register are used as a pointer to memory. The address pointed
to is the first byte of the address pointer
|
Memory indirect
|
The contents of memory provide a pointer to memory
|
Register indirect with index register
|
The
effective address is calculated by adding the values of the two registers
together.
|
Absolute address with index register
|
The effective address is calculated by adding the value of the index
register to the absolute address
|
Program Counter relative
|
The
effective address is calculated as an offset to the PC. This is one method
for making programs relocatable.
|
