SQ

SQ is esoteric programming language created by CatLooks without conditional jumps. The file with code must be exactly 32 Kb. Because a file is binary, source code can be compiled into one (compiler indev).

Code

SQ is designed to emulate 8-bit CPU (like 6502). There are lots of features that present in both.

Syntax

Source code resembles 6502 Assembly (most opcodes from 6502 are not present but there are few new ones). For example:

 label:
   lda #A9

There is one difference in syntax, namely no need for $ sign to mark hexadecimal numbers.

Registers

There are 6 registers to work with: A (Accumulator), B (Buffer), X (IndeX), I (Instruction pointer), S (Stack pointer), P (Processor status). All of them are 8-bit except for I (16-bit) and P (3-bit).

• Accumulator is used mainly for data transfer and math.
• Buffer is used to record Accumulator state and restore it later.
• Index is used to set offset for Accumulator load.
• Instruction pointer contains a pointer to current opcode.
• Stack pointer contains a pointer to current object on stack.
• Processor status contains some info about last operation details.

Status Register

When pushed to the stack, status register will have this form:

 -----NZC

• C - carry (usually math overflow bit or shifted out bit)
• Z - zero (set when number last accessed register is zero)
• N - negative (copy of bit 7 of last accessed register)

Parameter Modes

There are only 52 opcodes (from 256 available values) in SQ (often implied or with register). They are either followed by an argument, an argument with x or just single. Here's the list of all possible argument variations:

Name	Syntax	Bits	Description
Immediate (#)	#byte	000	Straight usage of the number.
Implied	-	001	No parameter.
Indirect (ind)	(word)	010	Value at address located at parameter address.
Indirect with X (ind, x)	(word, x)	011	Same as Indirect except parameter address is shifted with X.
Zeropage (zp)	byte	100	Value at first 256 bytes of address space (RAM).
Zeropage with X (zp, x)	byte, x	101	Same as Zeropage except address is shifted with X.
Absolute (abs)	word	110	Value at parameter address.
Absolute with X (abs, x)	word, x	111	Same as Absolute except address is shifted with X.

Note: unlike 6502, Zeropage with X mode can cross 256-byte page.

Opcodes

Here's the list of all opcodes in SQ:

Instruction	Opcode	Description
brk	00	Exits program.
lda #	A0	Loads A with direct value.
lda abs	A6	Loads A with value at address.
lda abs, x	A7	Loads A with value at address + X.
lda zp	A4	Loads A with value at zeropage address.
lda zp, x	A5	Loads A with value at zeropage address + X.
lda (ind)	A2	Loads A with value at address at address.
lda (ind, x)	A3	Loads A with value at address at (address + X).
lda (ind), x	AF	Loads A with value at (address at address) + X.
ldx #	E0	Loads X with direct value.
ldx abs	E6	Loads X with value at address.
ldx zp	E4	Loads X with value at zeropage address.
ldx (ind)	E2	Loads X with value at address at address.
sta abs	FE	Stores A at address.
sta abs, x	FF	Stores A at address + X.
sta zp	FC	Stores A at zeropage address.
sta zp, x	FD	Stores A at zeropage address + X.
sta (ind)	F2	Stores A at address at address.
stx abs	8E	Stores X at address.
stx zp	8C	Stores X at zeropage address.
stx (ind)	82	Stores X at address at address.
jmp abs	06	Loads I with 16-bit value.
jmp (ind, x)	03	Loads I with 16-bit value at address + X.
jsr abs	0E	Pushes I on the stack and jumps to address.
rts	09	Loads I with 16-bit value poped from the stack.
tab	41	Records value of A.
rea	51	Restores value of A.
lsr #	60	Shifts A right # times (shifted bit -> carry).
lsl #	68	Shifts A left # times (shifted bit -> carry).
lsr	61	Shifts A right 1 time (shifted bit -> carry).
lsl	69	Shifts A left 1 time (shifted bit -> carry).