blob: 73b588eff5eee80741c3644e60e0a34c42c57b4a (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
# 16-bit CPU design doc
## Features
16-bit data
16-bit address width
16-bit instruction width
MISC
4-bit opcodes
instruction format
xxxx xxxx xxxx xxxx - xxxx xxxx xxxx xxxx
General purpose registers:
000: Zero register
001: RA
010: RB
011: RC
100: RD
Special registers: MAR (memory address), IR (instruction), FR (flag)
Serial peripheral ports:
101: PA
110: PB
for communicating with the outside world.
Expansion port that connects directly to the main bus
Addressing mode: indirect absolute (addresses are stored in registers and point to a complete address)
## Operations
### Memory operations
Format: [ 4 opcode . 3 rt . 3 rx . 6 unused ]
ldr [rx] [rt] # load value from memory at address (register value) rx to rt
str [rx] [rt] # store value in rt to memory address (register value) rx
### Immediate operations
Format: [ 4 opcode . 3 reg . 9 imm ]
ldi [rt] [imm] # load immediate value imm to rt
### Nullary operations
Format: [ 4 opcode . 12 unused ]
hlt # halt
### Arithmetic and logic operations
Format [ 4 opcode . 3 rt . 3 rl . 3 rr . 3 alu S ]
alu [rl] [rr] [rt] [S] # compute rl ? rr where ? is the operation defined by
# 0SSS in the ALU, and store result in rt
# see datasheet of 74382 and ALU impl
als [rl] [rr] [rt] [S] # compute rl ? rr where ? is the operation defined by
# 1SSS in the ALU, and store result in rt
# see datasheet of 74382 and ALU impl
Note: mul, div, gt, lt, eq, neq are implemented as pseudoinstructions in the assembler
### Jump
Format: [ 4 opcode . 3 rx . 9 unused ]
jmp [rx] # Jump to address in register rx
### Branch
Format: [ 4 opcode . 1 unused . 2 flag . 9 addr ]
Branch if flag is set (where flag 0b00 = Z, 0b01 = C, ...)
br [flag] [addr]
Flags:
- C = ALU carry bit
- O = ALU overflow bit
- Z = ALU zero bit
- S = ALU sign bit
Interrupt lines: 1 (IRQ)
|
