Elmo HARSFEN0602, HARmonica software manual Op code structure and addressing modes, Short reference

HARSFEN0602ElmoHARmonicaSoftwareManual PRELIMINARYDRAFT

The virtual machine supports the following data types:

-INTEGER: 32 BIT SIGNED INTEGER

-Float: 32 bit IEEE floating point number (24 bit mantissa, 8 bit sign)

Logical operators yield Boolean results – True or False.

True is equivalent to the integer 1.

False is equivalent to the integer 0.

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7.5Op code structure and addressing modes

Op code it’s a bit filed (16 bits) which give us information about the VAC (Virtual Assembly Code) and it’s operands, more details in table below.

Each operand has an addressing mode indicates the location of the operand (stack, data segment, immediate).

Op code bit field:

Bits	Description		Meaning
0	ChangeStack		Flag shows whether SP should change (increase/decrease) after
			an execution of a VAC. This flag is ignored by some of the
			commands. 1 – change stack, 0 – don’t change.
1-7	CodeIndex		Index of VAC in table
8	OperType1		Data type of first operand . 1 – Float, 0 – Integer
9	OperType2		Data type of second operand
10-12	AddrMode1		Addressing mode of first operand (destination)
12-15	AddrMode2		Addressing mode of second operand (source)
Addressing Modes:
Addressing Mode
		MEANING
ABSENT		Lack operand after command code. Usually Operand is at
		the top of stack.
IMMEDIATE1		Operand is char integer and stated immediately after
		command code
IMMEDIATE2		Operand is short integer and stated immediately after
		command code
IMMEDIATE4		Operand is long integer or float and stated immediately
		after command code
MEM_DIRECT		Operand is at the memory address (ram) which stated after
		command code.
STACK_IMMEDIATELY		Operand stated at stack member which placed after
		command
BP_RELATIVE		Operand is placed in the stack relatively to the base
		pointer. Exact location in the stack is base pointer +
		operand stated after command code.

7.6Short reference

A concise reference is given in the table below.

OP code	Meaning
MLT	Multiply the top of stack with the number below.
SUB	Subtract the top of stack from the number below.
ADD	Add the top of stack to the number below.
DIV	Divide the number below top of stack by the top of stack.