Instructions

Chip16 Instructions

Abbrevations used

Abbreviations	Meaning		Abbreviations	Meaning		Abbreviations	Meaning
HH	high byte of a word		FG	screen foreground layer		[A]	value in memory at address A
LL	low byte of a word		BG	background color index		x	conditional code for jumps/calls
N	nibble (4-bit value)		hflip	horizontal sprite flip
X, Y, Z	4-bit register identifiers		vflip	vertical sprite flip

Setting flags

For the instructions marked as affecting flags:

• C is set:

  • for ADD - when the result would have imaginary bit[16] set; else it is cleared.
  • for SUB - when the operation needed to borrow from bit[16]; else it is cleared.
  • for MUL - when the result is too big to fit into 16 bits; else it is cleared.
  • for DIV - when the remainder of the division is non-zero; else it is cleared.
  • for DRW - when the new sprite overlaps any existing pixel (other than 0 - transparent); else it is cleared.

• Z is set:

  • when the result is 0, else its cleared.

• O is set:

  • in general, when the sign of the result differs from what would be expected.
  • for ADD: when the result is positive and both operands were negative, or if the result is negative and both operands were positive; else it is cleared.
  • for SUB (X-Y=Z): when Z is positive and X is negative and Y is positive, or if Z is negative and X is positive and Y is negative; else it is cleared.

• N is set:

  • when the result is less than 0 (bit[15] == 1); else it is cleared.

Conditional branch types

Branch when the flags requirements are met.

Type	Index	Flags requirements	Mnemonic
Z	0x0	Z == 1	Equal (Zero)
NZ	0x1	Z == 0	Not Equal (Non-Zero)
N	0x2	N == 1	Negative
NN	0x3	N == 0	Not-Negative (Positive or Zero)
P	0x4	N == 0 and Z==0	Positive
O	0x5	O == 1	Overflow
NO	0x6	O == 0	No Overflow
A	0x7	C == 0 and Z == 0	Above (Unsigned Greater Than)
AE	0x8	C == 0	Above Equal (Unsigned Greater Than or Equal)
B	0x9	C == 1	Below (Unsigned Less Than)
BE	0xA	C == 1 or Z == 1	Below Equal (Unsigned Less Than or Equal)
G	0xB	O == N and Z == 0	Signed Greater Than
GE	0xC	O == N	Signed Greater Than or Equal
L	0xD	O != N	Signed Less Than
LE	0xE	O != N or Z == 1	Signed Less Than or Equal
RES	0xF		Reserved for future use

Alternative valid mnemonics:

Type	Index	Flags requirements	Mnemonic
C	0x9	C == 1	Carry (Same as B)
NC	0x8	C == 0	Not Carry (Same as GE)

---

Note: PC is incremented by 4 after the instruction is read, and before it is executed.

0x - Misc/Video/Audio

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
00 00 00 00	NOP	No operation.		0.8
01 00 00 00	CLS	Clear FG, BG = 0.		0.8
02 00 00 00	VBLNK	Wait for VBlank. If (!vblank) PC -= 4;		0.8
03 00 0N 00	BGC N	Set background color to index N (0 is black).		0.8
04 00 LL HH	SPR HHLL	Set sprite width (LL) and height (HH).		0.8
05 YX LL HH	DRW RX, RY, HHLL	Draw sprite from address HHLL at (RX, RY).	C	0.8
06 YX 0Z 00	DRW RX, RY, RZ	Draw sprite from [RZ] at (RX, RY).	C	0.8
07 0X LL HH	RND RX, HHLL	Store random number in RX (max. HHLL).		0.8
08 00 00 00	FLIP 0, 0	Set hflip = false, vflip = false		0.8
08 00 00 01	FLIP 0, 1	Set hflip = false, vflip = true		0.8
08 00 00 02	FLIP 1, 0	Set hflip = true, vflip = false		0.8
08 00 00 03	FLIP 1, 1	Set hflip = true, vflip = true		0.8
09 00 00 00	SND0	Stop playing sounds.		0.8
0A 00 LL HH	SND1 HHLL	Play 500Hz tone for HHLL ms.		0.8
0B 00 LL HH	SND2 HHLL	Play 1000Hz tone for HHLL ms.		0.8
0C 00 LL HH	SND3 HHLL	Play 1500Hz tone for HHLL ms.		0.8
0D 0X LL HH	SNP RX, HHLL	Play tone from RX for HHLL ms.		1.1
0E AD SR VT	SNG AD, VTSR	Set sound generation parameters.		1.1

1x - Jumps (Branches)

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
10 00 LL HH	JMP HHLL	Set PC to HHLL.		0.8
11 00 LL HH	JMC HHLL	Jump to the specified address if carry flag is raised.		0.8
12 0x LL HH	Jx HHLL	If x, then perform a JMP.		0.9
13 YX LL HH	JME RX, RY, HHLL	Set PC to HHLL if RX == RY.		0.8
14 00 LL HH	CALL HHLL	Store PC to [SP], increase SP by 2, set PC to HHLL.		0.8
15 00 00 00	RET	Decrease SP by 2, set PC to [SP].		0.8
16 0X 00 00	JMP RX	Set PC to RX.		0.8
17 0x LL HH	Cx HHLL	If x, then perform a CALL.		0.9
18 0X 00 00	CALL RX	Store PC to [SP], increase SP by 2, set PC to RX.		0.8

2x - Loads

Loads from memory are always 16-bit.

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
20 0X LL HH	LDI RX, HHLL	Set RX to HHLL.		0.8
21 00 LL HH	LDI SP, HHLL	Set SP to HHLL.		0.8
22 0X LL HH	LDM RX, HHLL	Set RX to [HHLL].		0.8
23 YX 00 00	LDM RX, RY	Set RX to [RY].		0.8
24 YX 00 00	MOV RX, RY	Set RX to RY.		0.8

3x - Stores

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
30 0X LL HH	STM RX, HHLL	Set [HHLL] to RX.		0.8
31 YX 00 00	STM RX, RY	Set [RY] to RX.		0.8

4x - Addition

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
40 0X LL HH	ADDI RX, HHLL	Set RX to RX+HHLL.	C``Z``O``N	0.8
41 YX 00 00	ADD RX, RY	Set RX to RX+RY.	C``Z``O``N	0.8
42 YX 0Z 00	ADD RX, RY, RZ	Set RZ to RX+RY.	C``Z``O``N	0.8

5x - Subtraction

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
50 0X LL HH	SUBI RX, HHLL	Set RX to RX-HHLL.	C``Z``O``N	0.8
51 YX 00 00	SUB RX, RY	Set RX to RX-RY.	C``Z``O``N	0.8
52 YX 0Z 00	SUB RX, RY, RZ	Set RZ to RX-RY.	C``Z``O``N	0.8
53 0X LL HH	CMPI RX, HHLL	Compute RX-HHLL, discard result.	C``Z``O``N	0.8
54 YX 00 00	CMP RX, RY	Compute RX-RY, discard result.	C``Z``O``N	0.8

6x - Bitwise AND (&)

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
60 0X LL HH	ANDI RX, HHLL	Set RX to RX&HHLL.	Z``N	0.8
61 YX 00 00	AND RX, RY	Set RX to RX&RY.	Z``N	0.8
62 YX 0Z 00	AND RX, RY, RZ	Set RZ to RX&RY.	Z``N	0.8
63 0X LL HH	TSTI RX, HHLL	Compute RX&HHLL, discard result.	Z``N	0.8
64 YX 00 00	TST RX, RY	Compute RX&RY, discard result.	Z``N	0.8

7x - Bitwise OR (|)

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
70 0X LL HH	ORI RX, HHLL	Set RX to RX|HHLL.	Z``N	0.8
71 YX 00 00	OR RX, RY	Set RX to RX|RY.	Z``N	0.8
72 YX 0Z 00	OR RX, RY, RZ	Set RZ to RX|RY.	Z``N	0.8

8x - Bitwise XOR (^)

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
80 0X LL HH	XORI RX, HHLL	Set RX to RX^HHLL.	Z``N	0.8
81 YX 00 00	XOR RX, RY	Set RX to RX^RY.	Z``N	0.8
82 YX 0Z 00	XOR RX, RY, RZ	Set RZ to RX^RY.	Z``N	0.8

9x - Multiplication

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
90 0X LL HH	MULI RX, HHLL	Set RX to RX*HHLL	C``Z``N	1.1
91 YX 00 00	MUL RX, RY	Set RX to RX*RY	C``Z``N	0.8
92 YX 0Z 00	MUL RX, RY, RZ	Set RZ to RX*RY	C``Z``N	0.8

Ax - Division

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
A0 0X LL HH	DIVI RX, HHLL	Set RX to RX\HHLL	C``Z``N	0.8
A1 YX 00 00	DIV RX, RY	Set RX to RX\RY	C``Z``N	0.8
A2 YX 0Z 00	DIV RX, RY, RZ	Set RZ to RX\RY	C``Z``N	0.8
A3 0X LL HH	MODI RX, HHLL	Set RX to RX MOD HHLL	Z``N	1.3
A4 YX 00 00	MOD RX, RY	Set RX to RX MOD RY	Z``N	1.3
A5 YX 0Z 00	MOD RX, RY, RZ	Set RZ to RX MOD RY	Z``N	1.3
A6 0X LL HH	REMI RX, HHLL	Set RX to RX % HHLL	Z``N	1.3
A7 YX 00 00	REM RX, RY	Set RX to RX % RY	Z``N	1.3
A8 YX 0Z 00	REM RX, RY, RZ	Set RZ to RX % RY	Z``N	1.3

Bx - Logical/Arithmetic Shifts

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
B0 0X 0N 00	SHL RX, N	Set RX to RX << N	Z``N	0.8
B1 0X 0N 00	SHR RX, N	Set RX to RX >> N	Z``N	0.8
B0 0X 0N 00	SAL RX, N	Set RX to RX << N	Z``N	0.8
B2 0X 0N 00	SAR RX, N	Set RX to RX >> N, copying leading bit	Z``N	0.8
B3 YX 00 00	SHL RX, RY	Set RX to RX << RY	Z``N	0.8
B4 YX 00 00	SHR RX, RY	Set RX to RX >> RY	Z``N	0.8
B3 YX 00 00	SAL RX, RY	Set RX to RX << RY	Z``N	0.8
B5 YX 00 00	SAR RX, RY	Set RX to RX >> RY, copying leading bit	Z``N	0.8

Note that a left arithmetic shift is a left logical shift, since we are not expanding the leading bit.

Hence SAL is syntactic sugar, and maps to its corresponding SHL opcode.

Cx - Push/Pop

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
C0 0X 00 00	PUSH RX	Set [SP] to RX, increase SP by 2		0.8
C1 0X 00 00	POP RX	Decrease SP by 2, set RX to [SP]		0.8
C2 00 00 00	PUSHALL	Store R0..RF at [SP], increase SP by 32		0.8
C3 00 00 00	POPALL	Decrease SP by 32, load R0..RF from [SP]		0.8
C4 00 00 00	PUSHF	Set [SP] to FLAGS, increase SP by 2		1.1
C5 00 00 00	POPF	Decrease SP by 2, set FLAGS to [SP]		1.1

Dx - Palette

Opcode (Hex)	Mnemonic	Usage	Flags affected	Introduced
D0 00 LL HH	PAL HHLL	Load palette from [HHLL]		1.1
D1 0X 00 00	PAL RX	Load palette from [RX]		1.1

Ex - Not/Neg

Opcode	Mnemonic	Meaning	Flags affected	Introduced
E0 0X LL HH	NOTI RX, HHLL	Set RX to NOT HHLL	Z``N	1.3
E1 0X 00 00	NOT RX	Set RX to NOT RX	Z``N	1.3
E2 YX 00 00	NOT RX, RY	Set RX to NOT RY	Z``N	1.3
E3 0X LL HH	NEGI RX, HHLL	Set RX to NEG HHLL	Z``N	1.3
E4 0X 00 00	NEG RX	Set RX to NEG RX	Z``N	1.3
E5 YX 00 00	NEG RX, RY	Set RX to NEG RY	Z``N	1.3