TetraBit

TetraBit is an esoteric assembly language I designed which uses a slightly 4 Bits, 8 Bytes aesthetic, however with different instructions and unlimited program size. You can write it in either assembly- or machine-code style. There are 16 memory addresses, 0-15 (or F) and they are split up like this:

• Addresses 0-6 are the 7 free variables.
• Addresses 7-E make up a 4x2 screen.
• Address F is a read-only which holds one random value, 0-F, changing every instruction.

Opcodes

Instruction	6502-esque description
0	NOP instruction. Mainly there to fill lines, however it also updates the screen.
1 X Y	STA. Stores the value X at address Y.
2 X	LDA. Loads the value at address X.
3 X Y	INC. Increments the value at address X by Y.
4 X Y	DEC. Decrements the value at address X by Y.
5 X Y	MOD. Turns the value at address X into itself modulo Y.
6 X	ACT. Turns the value at address X into 9*X + 1, modulo 16.
7 X Y	AND. Logical-ANDs the value at address X with value Y.
8 X Y	ORA. Logical-ORs the value at address X with value Y.
9 X Y	XOR. Logical-XORs the value at address X with value Y.
10 (or A) X	NOT. Bitwise NOTs the value at address X.
B X Y	BEQ. Branches if the value at address X and value Y are equal.
C X	"DSR". Defines a subroutine with label value X.
D	"ENS". Ends the current subroutine being defined or used (subroutines are implicit when inside BEQs).
E X	"CSR". Calls the subroutine with label value X.
F	HLT/END. Halts the program.

An example of using BEQ correctly (linebreaks added for readability):

B 5 0
3 5 1 ; if true
D     ; end true subroutine
3 5 2 ; if false
D     ; end false subroutine
D     ; merge branches by ending branch subroutine
F     ; end program (must go at end of full program)

Here it is without linebreaks, as machine code in TetraBit:

B 5 0 3 5 1 D 3 5 2 D D F

The memory is visualized like this:

0 1 2 3 4 5 6
      / \
789A | F |
BCDE  \ /

Now how must 0-F look as colors on the screen? Like this.

Colors

Value	RGB color (3-bit when possible)
0	#000
1	#808080
2	#00f
3	#8080ff
4	#0f0
5	#80ff80
6	#0ff
7	#80ffff
8	#f00
9	#ff8080
A	#f0f
B	#ff80ff
C	#ff0
D	#ffff80
E	#fff

F is transparent, so on some interfaces it will be white, on others black, depending on how it is handled. It may also be a light-gray/white checkerboard, a common pattern to show transparency.

Example programs

Multiplies two values together:

C 0 2 3 3 3 1 4 2 1 D 2 0 2 2 1 1 2 3 1 2 E 0 F

Or, more readably:

C 0   ; define subroutine 0 as:
2 3   ; load address 3
3 3 1 ; increment address 3 by 1
4 2 1 ; decrement address 2 by 1
D     ; end subroutine           ;; (definition's end)
2 0   ; load address 0
2 2 1 ; store 2 at address 1
1 2   ; load address 2
3 1 2 ; increment address 1 by 2
E 0   ; call subroutine 0
F     ; end

Paints a hard-coded checkerboard of blue and cyan pixels:

1 2 7 1 2 9 1 2 C 1 2 E 1 6 8 1 6 A 1 6 B 1 6 D F

Or:

1 2 7
1 2 9
1 2 C
1 2 E
1 6 8
1 6 A
1 6 B
1 6 D
F