Unit 4 - Assembly language

Different stages for a two-pass assembler

• Lines are read one at a time (1st and 2nd pass)

• Comments are removed, remove white space, add labels to the symbol table (1st pass)

• Check opcode is in the instruction set (1st pass)

• Generate the object code (2nd pass)

Different groups in instruction sets

• Data movement

• Input and output of data

• Arithmetic operations

• Unconditional and conditional instructions

• Compare instructions

Data movement

Data is moved or copied from register to another

Arithmetic operations

Perform addition and subtraction

Compare instructions

Compare the result to another value

Input and output of data

• Takes an input from the user

• Outputs the character of the binary number

Unconditional and conditional instructions

Move another instruction (identified by a label)

Immediate addressing

The operand(number enterred) is the actual value that is operated on

Direct addressing

The operand is the memory address where the value is held (the input is the address of the data to be used)

Indirect addressing

The address to be used is at the given address

• The number entered is an address - this address holds the address of the data

Indexed addressing

Form the address from the given address plus the content of the index register

Relative addressing

The address to be used is an offset number of locations away, relative to the address of the current location