Difference between revisions of "Opcode"
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Latest revision as of 21:20, 26 August 2024
The CPU of a digital computer responds to a series of ones and zeros read from memory. The pattern of these, that determine what the CPU is supposed to do, are called Operation Codes or opcode. As an example the opcode $2B on the F8 System means No Operation (NOP). Programs are made up of opcodes which instruct the F8 System to do something, such as load a register with a value, perform arithmetic on a register, change the program counter (jump) or input or output data through the ports.
Opcodes in the F8 System are each one byte wide, though some may be followed by an address (two bytes) or a value for the opcode to use, these extra bytes are called operands and an opcode with its operand is called an instruction and the complete set for a CPU is called an Instruction Set.
Instead of programming these numbers directly (Machine Code Programming) programmers came up with the mnemonic names and wrote programs to translate such code into machine code. This mnemonic form of programming is called Assembly Language. Below is a table showing both types, if you choose Assembly Language then DASM or f8tool are free Assemblers for the F8 System.
The Instruction Set
In the information for each opcode, the following notations are used:
| Opcode Notations | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| A | Accumulator | ||||||||
| Ri | First registers i (r0-r11 [HU,HL=r10,11]) | ||||||||
| P0 | Program counter (PC0) | ||||||||
| P | Program counter Stack (PC1) | ||||||||
| DC0 | Data counter | ||||||||
| DC1 | Data counter storage | ||||||||
| W | Status register (x,x,x,ICB,O,Z,C,S) Exhange only via the J register (R9) | ||||||||
| ISAR | Indirect Scratchpad Address Register | ||||||||
| r | Scratchpad addressing as:
| ||||||||
| t | 3-bit constant | ||||||||
| i | 4-bit constant | ||||||||
| n | 8-bit constant | ||||||||
| mn | 16-bit constant | ||||||||
| ( ) | Contents of register (e.g.(R11) or (DC)) | ||||||||
| x | Binary value placeholder | ||||||||
| Status Flag Notations | |||||||||
| ICB | Interrupts Allowed Flag, b4 in W | ||||||||
| O | Overflow Flag, b3 in W | ||||||||
| Z | Zero Flag, b2 in W | ||||||||
| C | Carry Flag, b1 in W | ||||||||
| S | Sign Flag, b0 in W | ||||||||
| 0 | Resets status flag | ||||||||
| 1 | Sets status flag | ||||||||
| X | Modifies status flag | ||||||||
| Mnemonic | Length | Cycles | Description | Opcode | Status Flags | Cycle | ROMC state | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Binary | Hex | O | Z | C | S | ||||||
| LR A, KU | 1 | 1 | A ← (KU)[r12] | %00000000 | $00 | - | - | - | - | S | 0 |
| LR A, KL | 1 | 1 | A ← (KL)[r13] | %00000001 | $01 | - | - | - | - | S | 0 |
| LR A, QU | 1 | 1 | A ← (QU)[r14] | %00000010 | $02 | - | - | - | - | S | 0 |
| LR A, QL | 1 | 1 | A ← (QL)[r15] | %00000011 | $03 | - | - | - | - | S | 0 |
| LR KU, A | 1 | 1 | [r12]KU ← (A) | %00000100 | $04 | - | - | - | - | S | 0 |
| LR KL, A | 1 | 1 | [r13]KL ← (A) | %00000101 | $05 | - | - | - | - | S | 0 |
| LR QU, A | 1 | 1 | [r14]QU ← (A) | %00000110 | $06 | - | - | - | - | S | 0 |
| LR QL, A | 1 | 1 | [r15]QL ← (A) | %00000111 | $07 | - | - | - | - | S | 0 |
| LR K, P | 1 | 4 | [r12]KU ← (PC1U) [r13]KL ← (PC1L) |
%00001000 | $08 | - | - | - | - | L L S |
7 B 0 |
| LR P, K | 1 | 4 | PC1U ← (KU)[r12] PC1L ← (KL)[r13] |
%00001001 | $09 | - | - | - | - | L L S |
15 18 0 |
| LR A, IS | 1 | 1 | A ← (ISAR) | %00001010 | $0A | - | - | - | - | S | 0 |
| LR IS, A | 1 | 1 | ISAR ← (A) | %00001011 | $0B | - | - | - | - | S | 0 |
| PK | 1 | 2.5 | PC1 ← (PC0) PC0L ← (KL)[r13] PC0U ← (KU)[r12] |
%00001100 | $0C | - | - | - | - | L L S |
12 14 0 |
| LR P0, Q | 1 | 4 | PC0L ← (QL)[r15] PC0U ← (QU)[r14] |
%00001101 | $0D | - | - | - | - | L L S |
17 14 0 |
| LR Q, DC | 1 | 4 | [r14]QU ← (DC0U) [r15]QL ← (DC0L) |
%00001110 | $0E | - | - | - | - | L L S |
6 9 0 |
| LR DC, Q | 1 | 4 | DC0U ← (QU)[r14] DC0L ← (QL)[r15] |
%00001111 | $0F | - | - | - | - | L L S |
16 19 0 |
| LR DC, H | 1 | 4 | DC0U ← (R10) DC0L ← (R11) |
%00010000 | $10 | - | - | - | - | L L S |
16 19 0 |
| LR H, DC | 1 | 4 | R10 ← (DC0U) R11 ← (DC0L) |
%00010001 | $11 | - | - | - | - | L L S |
6 9 0 |
| SR 1 | 1 | 1 | Shift (A) right one bit, fill with %0 | %00010010 | $12 | 0 | X | 0 | 1 | S | 0 |
| SL 1 | 1 | 1 | Shift (A) left one bit, fill with %0 | %00010011 | $13 | 0 | X | 0 | X | S | 0 |
| SR 4 | 1 | 1 | Shift (A) right four bits, fill with %0000 | %00010100 | $14 | 0 | X | 0 | 1 | S | 0 |
| SL 4 | 1 | 1 | Shift (A) left four bits, fill with %0000 | %00010101 | $15 | 0 | X | 0 | X | S | 0 |
| LM | 1 | 2.5 | A ← ((DC0)) DC0 ← DC0 + 1 |
%00010110 | $16 | - | - | - | - | L S |
2 0 |
| ST | 1 | 2.5 | DC0 ← (A) DC0 ← DC0 + 1 |
%00010111 | $17 | - | - | - | - | L S |
5 0 |
| COM | 1 | 1 | A ← (A)⊕$FF [invert/complement] |
%00011000 | $18 | 0 | X | 0 | X | S | 0 |
| LNK | 1 | 1 | A ← (A)+(C) (add carry from previous operation) |
%00011001 | $19 | X | X | X | X | S | 0 |
| DI | 1 | 1 | Disable interrupts status register bit 4 |
%00011010 | $1A | - | - | - | - | S S |
1C 0 |
| EI | 1 | 1 | Enable interrupts status register bit 4 |
%00011011 | $1B | - | - | - | - | S S |
1C 0 |
| POP | 1 | 2 | PC0 ← (PC1) | %00011100 | $1C | - | - | - | - | S S |
4 0 |
| LR W, J | 1 | 1 | W ← (R9) | %00011101 | $1D | - | - | - | - | S S |
1C 0 |
| LR J, W | 1 | 2 | R9 ← (W) | %00011110 | $1E | - | - | - | - | S | 0 |
| INC | 1 | 1 | A ← (A)+1 | %00011111 | $1F | X | X | X | X | S | 0 |
| LI n | 2 | 2.5 | A ← n | %00100000 %xxxxxxxx | $20 $xx | - | - | - | - | L S |
3 0 |
| NI n | 2 | 2.5 | A ← (A) AND n | %00100001 %xxxxxxxx | $21 $xx | 0 | X | 0 | X | L S |
3 0 |
| OI n | 2 | 2.5 | A ← (A) OR n | %00100010 %xxxxxxxx | $22 $xx | 0 | X | 0 | X | L S |
3 0 |
| XI n | 2 | 2.5 | A ← (A)⊕n | %00100011 %xxxxxxxx | $23 $xx | 0 | X | 0 | X | L S |
3 0 |
| AI n | 2 | 2.5 | A ← (A)+n | %00100100 %xxxxxxxx | $24 $xx | X | X | X | X | L S |
3 0 |
| CI n | 2 | 2.5 | n+!(A)+1 (n-A) Only set status |
%00100101 %xxxxxxxx | $25 $xx | X | X | X | X | L S |
3 0 |
| IN n | 2 | 4 | Data Bus ← Port n A ← (Port n) |
%00100110 %xxxxxxxx | $26 $xx | 0 | X | 0 | X | L L S |
3 1B 0 |
| OUT n | 2 | 4 | Data Bus ← Port n Port n ← (A) |
%00100111 %xxxxxxxx | $27 $xx | - | - | - | - | L L S |
3 1A 0 |
| PI mn | 3 | 6.5 | A ← m PC1 ← (PC0)+1 PC0L ← n PC0U ← (A) [A is destroyed] |
%00101000 %xxxxxxxx %xxxxxxxx | $28 $xx $xx | - | - | - | - | L S L L S |
3 D C 14 0 |
| JMP mn | 3 | 5.5 | A ← m PC0L ← n PC0U ← (A) [A is destroyed] |
%00101001 %xxxxxxxx %xxxxxxxx | $29 $xx $xx | - | - | - | - | L L L S |
3 c 14 0 |
| DCI mn | 3 | 6 | DC0U ← m PC0+1 DC0L ← n PC0+1 |
%00101010 %xxxxxxxx %xxxxxxxx | $2A $xx $xx | - | - | - | - | L S L S S |
11 3 E 3 0 |
| NOP | 1 | 1 | No operation (cycle waster) |
%00101011 | $2B | - | - | - | - | S | 0 |
| XDC | 1 | 2 | DC0,DC1 ← DC1,DC0 | %00101100 | $2C | - | - | - | - | S S |
1D 0 |
| DS r | 1 | 1.5 | r ← (r)+$FF [decrease scratchpad byte] |
%0011xxxx | $3x | X | X | X | X | L | 0 |
| LR A, r | 1 | 1 | A ← (r) | %0100xxxx | $4x | - | - | - | - | S | 0 |
| LR A, HU | 1 | 1 | A ← (HU) | %01001010 | $4A | - | - | - | - | S | 0 |
| LR A, HL | 1 | 1 | A ← (HL) | %01001011 | $4B | - | - | - | - | S | 0 |
| LR r, A | 1 | 1 | r ← (A) | %0101xxxx | $5x | - | - | - | - | S | 0 |
| LR HU, A | 1 | 1 | HU ← (A) | %01011010 | $5A | - | - | - | - | S | 0 |
| LR HL, A | 1 | 1 | HL ← (A) | %01011011 | $5B | - | - | - | - | S | 0 |
| LISU i | 1 | 1 | ISARU ← i | %01100xxx | $6x | - | - | - | - | S | 0 |
| LISL i | 1 | 1 | ISARL ← i | %01101xxx | $6x | - | - | - | - | S | 0 |
| CLR | 1 | 1 | A←0 | %01110000 | $70 | - | - | - | - | S | 0 |
| LIS i | 1 | 1 | A ← i | %0111xxxx | $7x | - | - | - | - | S | 0 |
| BT t, n | 2 | 3 (no branch) 3.5 (branch) |
AND bitmask t with W if result is not 0: PC0←PC0+n+1 See table below |
%10000xxx %xxxxxxxx | $8x $xx | - | - | - | - | S S S S L S |
1C 3 0 1C 1 0 |
| BP n | 2 | 3 (no branch) 3.5 (branch) |
if POSITIVE (sign bit 0): PC0←PC0+n+1 |
%10000001 %xxxxxxxx | $81 $xx | - | - | - | - | ||
| BC n | 2 | 3 (no branch) 3.5 (branch) |
if CARRY: PC0←PC0+n+1 |
%10000010 %xxxxxxxx | $82 $xx | - | - | - | - | ||
| BZ n | 2 | 3 (no branch) 3.5 (branch) |
if ZERO: PC0←PC0+n+1 |
%10000100 %xxxxxxxx | $84 $xx | - | - | - | - | ||
| AM | 1 | 2.5 | A ← (A)+((DC0)) DC0+1 |
%10001000 | $88 | X | X | X | X | L S |
2 0 |
| AMD | 1 | 2.5 | A ← (A)+((DC0)) decimal adjusted DC0+1 |
%10001001 | $89 | X | X | X | X | L S |
2 0 |
| NM | 1 | 2.5 | A ← (A)AND((DC0)) DC0+1 |
%10001010 | $8A | 0 | X | 0 | X | L S |
2 |
| OM | 1 | 2.5 | A ← (A)OR((DC0)) DC0+1 |
%10001011 | $8B | 0 | X | 0 | X | L S |
2 0 |
| XM | 1 | 2.5 | A ← (A)⊕((DC0)) DC0+1 |
%10001100 | $8C | 0 | X | 0 | X | L S |
2 0 |
| CM | 1 | 2.5 | ((DC0))-A only set status DC0+1 |
%10001101 | $8D | X | X | X | X | L S |
2 0 |
| ADC | 1 | 2.5 | DC0 ← (DC0)+(A) | %10001110 | $8E | - | - | - | - | L S |
A 0 |
| BR7 n | 2 | 2 (no branch) 2.5 (branch) |
if ISARL != 7: PC0 ← (PC0) + n +1 | %10001111 %xxxxxxxx | $8F $xx | - | - | - | - | S S L S |
3 0 1 0 |
| BR n | 2 | 3.5 | PC0 ← (PC0)+n+1 | %10010000 %xxxxxxxx | $90 $xx | - | - | - | - | ||
| BF i, n | 2 | 3 (no branch) 3.5 (branch) |
AND bitmask i with W if result = FALSE: PC0 ← (PC0)+n+1 See table below |
%1001xxxx %xxxxxxxx | $9x $xx | - | - | - | - | S L S S S S |
1C 1 0 1C 3 0 |
| BM n | 2 | 3 (no branch) 3.5 (branch) |
if NEGATIVE: PC0 ← (PC0)+n+1 |
%10010001 %xxxxxxxx | $91 $xx | - | - | - | - | ||
| BNC n | 2 | 3 (no branch) 3.5 (branch) |
if NO CARRY: PC0 ← (PC0)+n+1 |
%10010010 %xxxxxxxx | $92 $xx | - | - | - | - | ||
| BNZ n | 2 | 3 (no branch) 3.5 (branch) |
if NOT ZERO: PC0 ← (PC0)+n+1 |
%10010100 %xxxxxxxx | $94 $xx | - | - | - | - | ||
| BNO n | 2 | 3 (no branch) 3.5 (branch) |
if NO OVERFLOW: PC0 ← (PC0)+n+1 |
%10011000 %xxxxxxxx | $98 $xx | - | - | - | - | ||
| INS i | 1 | 2 (i=0-1) 4 (i=2-15) |
A ← (Port i) if i=2-15: Data Bus ← Port Address A ← (Port i) |
%1010xxxx | $Ax | 0 | X | 0 | X | p0/1: S, S p4-F: L, L, S |
p0/1: 1C, 0 p4-F: 1C, 1B, 0 |
| OUTS i | 1 | 2 (i=0-1) 4 (i=2-15) |
Port i ← (A) if i=2-15: Data Bus ← Port Address Port i ← (A) |
%1011xxxx | $Bx | - | - | - | - | p0/1: S, S p4-F: L, L, S |
p0/1: 1C, 0 p4-F: 1C, 1A, 0 |
| AS r | 1 | 1 | A ← (A)+(r) | %1100xxxx | $Cx | X | X | X | X | S | 0 |
| ASD r | 1 | 2 | A ← (A)+(r) (decimal) |
%1101xxxx | $Dx | X | X | X | X | S S |
1C 0 |
| XS r | 1 | 1 | A ← (A)⊕(r) | %1110xxxx | $Ex | 0 | X | 0 | X | S | 0 |
| NS r | 1 | 1 | A ← (A)AND(r) | %1111xxxx | $Fx | 0 | X | 0 | X | S | 0 |
| IRQ | 5.5 | PC0L ← Int address(l) PC0U ← Int.Address(u) PC1<-PC0 |
- | - | - | - | L L L S |
1C 0F 13 0 | |||
| RESET | 3.5 | PC0 ← 0 PC1 ← PC0 |
- | - | - | - | S L S |
1C 8 0 | |||
The BT instruction
| Branch conditions for BT instruction | |||||
|---|---|---|---|---|---|
| Operand t |
Status flags tested | Definition |
Comments | ||
| zero | carry | sign | |||
| 0 | 0 | 0 | 0 | Do not branch | An effective 3 cycle NO-OP |
| 1 | 0 | 0 | 1 | Branch if Positive | Same as BP |
| 2 | 0 | 1 | 0 | Branch on Carry | Same as BC |
| 3 | 0 | 1 | 1 | Branch if Carry or on Positive |
|
| 4 | 1 | 0 | 0 | Branch if Zero | Same as BZ |
| 5 | 1 | 0 | 1 | Branch if Zero or Positive |
Same as t=1 |
| 6 | 1 | 1 | 0 | Branch if Zero or on Carry |
|
| 7 | 1 | 1 | 1 | Branch if Zero, Carry or Positive |
Same as t=3 |
The BF instruction
| Branch conditions for BF instruction | ||||||
|---|---|---|---|---|---|---|
| Operand t |
Status flags tested | Definition |
Comments | |||
| ovf | zero | carry | sign | |||
| 0 | 0 | 0 | 0 | 0 | Unconditional branch relative |
Same as BR |
| 1 | 0 | 0 | 0 | 1 | Branch on negative | Same as BM |
| 2 | 0 | 0 | 1 | 0 | Branch if no carry | Same as BNC |
| 3 | 0 | 0 | 1 | 1 | Branch if no carry and negative |
|
| 4 | 0 | 1 | 0 | 0 | Branch if not zero | Same as BNZ |
| 5 | 0 | 1 | 0 | 1 | Same as t=1 | |
| 6 | 0 | 1 | 1 | 0 | Branch if no carry and not zero |
|
| 7 | 0 | 1 | 1 | 1 | Same as t=3 | |
| 8 | 1 | 0 | 0 | 0 | Branch if there is no overflow |
Same as BNO |
| 9 | 1 | 0 | 0 | 1 | Branch if negative and no overflow |
|
| A | 1 | 0 | 1 | 0 | Branch if no overflow and no carry |
|
| B | 1 | 0 | 1 | 1 | Branch if no overflow, no carry & negative |
|
| C | 1 | 1 | 0 | 0 | Branch if no overflow and not zero |
|
| D | 1 | 1 | 0 | 1 | Same as t=9 | |
| E | 1 | 1 | 1 | 0 | Branch if no overflow, no carry & not zero |
|
| F | 1 | 1 | 1 | 1 | Same as t=B | |
