1.1.1 structure and function of processor

• allow humans to input instructions easily without having to remember long strings of binary (1’s and 0’s). • allows programmer to write machine code (MC) using set of mnemonics that represent binary equivalent in MC • quicker/more efficent to translate to MC • makes more efficent use of CPU / system resources • programmer may want direct control over hardware/memory to access machine specific functionality • code written specifically for architecture • complier/interpreter may not be available

• Simplified instructions, used in assembly language, to easily write instructions.

• ADD, SUB, STA (store), LDA(load), BRA (branch always), BRZ(branch if zero), BRP(branch if positive), INP, OUT, HLT (end), DAT(data location), AVG.

• Ends the program

• Adds contents stored in specified memory location (uses operand) to value held in accumulator

• Subtracts contents stored in specified memory location using operand from value held in accumulator

• Always branches to address specified by operand. Unconditional branch

Branches to address specified by operand if value in accumulator = zero. Conditional branch

• branches to address specified by operand if value in accumulator is 0 or positive. A conditional branch

• Copies value held in accumulator to be stored in memory location specified by operand

Loads/copies value from specified memory location given by operand into accumulator

Takes an input value from input area and stores into accumulator (opcode is 9 and operand is 01)

• Displays value held in accumulator in output area (opcode is 9 and operand is 02)

• indicate a location that contains data and an optional value for instruction (initialisation: it creates a variable identifier that can be used instead of an address in instructions).

• Data definitions go at bottom of program

• it will map a memory location to identifier num1 and set its initial value as 100.

• opcode

• operand

• value in operand is referencing address in memory where the required value is located

• data to be used is the actual value of the operand. • often denoted with # in assembly language.

• value in operand is a reference to memory location that contains address in memory where required value is located

• large address ranges can be used to reference data and instructions

• index register = dedicated registers in the CPU. • Indexed referencing makes use of this register to access array with data in contiguous memory locations.

• operand specifies that memory location to be used is 10. it finds value in location and adds value in index register to that value (10+3=13) • therefore go to memory address 13 to access data to add.