Balaurul Unu

A virtual 12-bit educational microcomputer. Written by Chris Musei-Sequeira

Live at https://cjsequeira.github.io/balaurul/

Inspirations

• The Altair 8800 and s2js Altair 8800 online simulator
• Baulari in Romanian folklore
• Ben Eater's 8-bit CPU
• Daniel Grießhaber's SAP-1
• The Intel 8080 Microcomputer System User's Manual published September 1975
• Marco Schweighauser's Simple 8-Bit Assembler Simulator
• The PDP-11 and PDP-12 minicomputers

Coming next?

• SOUND? (Probably not)

Instructions (octal)

0000 - 0007: Special instructions

Opcode	Mnemonic	Description	Operand (If Any)	Width (Words)	Num. of Machine Cycles
0000	NOP	No operation		1	3
0001	HLT	Increment PC and halt CPU		1	4
0002	OUT	Write accumulator to OUT and draw the associated UTF-16 character on screen		1	4
0003	IN	Read input switches to accumulator		1	4
0004	KEY	Read keyboard to accumulator. Supported keys: Backspace, Tab, Enter, Escape, and printable characters		1	4
0005 - 0007		(Reserved)

0010 - 0017: No-operand instructions

Opcode	Mnemonic	Description	Operand (If Any)	Width (Words)	Num. of Machine Cycles
0010	INC	Increment accumulator		1	4
0011	DEC	Decrement accumulator		1	4
0012	ROL	Rotate accumulator left		1	4
0013	RCL	Rotate accumulator left through carry		1	4
0014	ROR	Rotate accumulator right		1	4
0015	RCR	Rotate accumulator right through carry		1	4
0016 - 0017		(Reserved)

0020 - 0037: Immediate-with-accumulator instructions

Opcode	Mnemonic	Description	Operand (If Any)	Width (Words)	Num. of Machine Cycles
0020	LDI	Load accumulator from immediate	Immediate value	2	5
0021	ADI	Add immediate to accumulator	Immediate value	2	6
0022	ACI	Add immediate plus carry to accumulator	Immediate value	2	6
0023	SUI	Subtract immediate from accumulator	Immediate value	2	6
0024	SBI	Subtract immediate from accumulator with borrow	Immediate value	2	6
0025	ANI	AND immediate value with accumulator	Immediate value	2	6
0026	ORI	OR immediate value with accumulator	Immediate value	2	6
0027	XOI	XOR immediate value with accumulator	Immediate value	2	6
0030	CMI	Compare accumulator with immediate	Immediate value	2	6
0031 - 0037		(Reserved)

0040 - 0057: Memory-with-accumulator instructions

Opcode	Mnemonic	Description	Operand (If Any)	Width (Words)	Num. of Machine Cycles
0040	LDA	Load accumulator from address	Address	2	6
0041	ADA	Add value at address to accumulator	Address	2	7
0042	ACA	Add value at address, plus carry, to accumulator	Address	2	7
0043	SUA	Subtract value at address from accumulator	Address	2	7
0044	SBA	Subtract value at address from accumulator with borrow	Address	2	7
0044	ANA	AND value at address with accumulator	Address	2	7
0045	ORA	OR value at address with accumulator	Address	2	7
0047	XOA	XOR value at address with accumulator	Address	2	7
0050	CMA	Compare value at address with accumulator	Address	2	7
0051	STA	Store accumulator to address	Address	2	6
0052	LDP	Load accumulator from address in pointer	Pointer address	2	8
0053	STP	Store accumulator at address in pointer	Pointer address	2	8
0054 - 0057		(Reserved)

0060 - 0077: Jump instructions

Opcode	Mnemonic	Description	Operand (If Any)	Width (Words)	Num. of Machine Cycles
0060	JMP	Unconditionally jump to address	Address	2	4
0061	JC	Jump to address if carry flag set	Address	2	4
0062	JZ	Jump to address if zero flag set	Address	2	4
0063	JNC	Jump to address if carry flag not set	Address	2	4
0064	JNZ	Jump to address if zero flag not set	Address	2	4
0065	CALL	Call subroutine at address	Address	2	6
0066	RET	Return from subroutine		1	5
0067	LPC	Load PC with value in accumulator		1	3
0070 - 0077		(Reserved)

Version history

• 1.0.0: Initial version