1.2 Systems software & development

Assembly language

Short, precise commands that provide greater control over the computer’s components.

Little Man Computer

A computer architecture that uses opcodes for low level instructions.

HLT

Opcode that stops program execution.

ADD

Opcode that adds the contents of a memory address to the accumulator.

SUB

Opcode that subtracts the contents of a memory address from the accumulator.

STA

Opcode that stores the contents of the accumulator in a memory address.

LDA

Opcode that loads the accumulator with the contents of a memory address.

BRA

Opcode that branches to a given address, always.

BRZ

Opcode that branches to a given address, if the accumulator is zero.

BRP

Opcode that branches to a given address, if the accumulator is zero or positive.

INP

Opcode that asks the user for a number and puts it into the accumulator.

OUT

Opcode that outputs the contents of the accumulator.

DAT

Opcode that stores data in a variable, declared.

OTC

Opcode that outputs a character in ASCII.

Addressing modes

Different types of addressing modes used in programming languages.

Direct

Addressing mode that takes the data from the contents of the memory location addressed.

Indirect

Addressing mode that takes the data from the address of the contents of the memory location addressed.

Immediate

Addressing mode that takes the data from the value addressed.

Indexed

Addressing mode that takes the data held in the memory location of the address + the index.

Symbolic

Addressing mode that takes the data held in a tag.