Assembly Language

• Mnemonics that are used for instructions depend on the processor being used - each processor has its own instruction set
• These are either RISC or CISC
• An instruction set is the pattern of 0s and 1s that a particular processor recognises as commands along with their associated meaning

• CMP r1, #10 compares the value in register 1 with the value 10

This consists of 4 parts:

• Operation Code- Uses letters to hekp explain what the command does (aka Opcode)
• Operands- The number of operands following an opcode depends on what the code is/does. Operands can be values, memory locations, general purpose registers.
• Addressing Mode- In the example above the # indicates that the data following is an actual value
• Comment- Optional but recommended as assembly language is much more difficult to follow.

• Direct Addressing- This mode tells the CPU which address contains the data contains the data you want to access.

Example: LDR R1, 100 <- Would copy the datain memory location 100 into register 1

• Immediate Addressing- This loads the data directly. The operand contains the actual number

Example: MOV R1, #10 <- Would move the value 10 into register 1

4 types of Operation Code:

• Arthimetic Operations
• Data Transfer Operations
• Logical Operations
• Branch Operations

• Add, Subtract, Multiply, Divide, Increment, Decrement
• ADD R0, R1, #03 <- Add 3 to R1 and store in R0
• SUB R0, R1, #03 <- Subtract 3 from R1 and store in R0

• Compare- two values for less than, greater than etc. (CMP)
• Negate- Reverse the sign

Shift- left and right binary positions

• Logical Shift- Moves One e.g. [10010] -> [00100] (with carry)
• Rotate =Shift- Flips (LSB becomes MSB) e.g. [10010] -> [01101]

• Status Register is udes to record certain features of a calculation (has it generated an overflow, is result negative/zero etc.)

• Moves data between registers and main memory
• MOV (Move), STR (Store), LDR (Load)

• Bitwise AND, OR, NOT and XOR
• Each bit in a bit string is compared with the corresponding bit in another bit string of the same length
• Can be used to compare and calculate values as well as mask out values

• This allows programs to not be linear
• BNE = Branch if not equal
• BEQ = Branch if equal
• BGT = Branch if greater than
• BLT = Branch if less than
• The results of the last comparison will be used to determine whether you will jump or not
• You will need a label to tell the program where to jump to
• Using a high level language hides the complexity of assembly langauge