Assembly Language

Example Programs

Assembly Language IF

Assembly Language DO WHILE

Operands

The operand can be interpreted in two different ways, if it uses:

• # it refers to a specific value to use
• Rm uses the value stored in register m

Op Codes

Below is a list of the OpCodes used within your examinations. This table will always be given to you with a small explanation and syntax for each command.

LDR - Load

This instruction is to load a value stored in memory into a CPU register.

LDR Rd, <memory ref>

STR - Store

This instruction is to store a value from Register d into Memory location <memory ref>.

STR Rd, <memory ref>

ADD - Add

Operation used to add two numbers together, the value in the operand to the value in Register n.

The output is stored in Register d

ADD Rd, Rn, <operand>

SUB - Subtract

operation used to subtract two numbers from each other, the value in the operand from the value in Register n.

The output is stored in Register d

SUB Rd, Rn, <operand>

MOV - Move

This instruction is to copy a value into a register. The value from the operand is stored in Register d

MOV Rd, <operand>

CMP - Compare

The CMP instruction compares two operands. It is generally used in conditional execution and is needed if you wish to do a conditional branch. It compares the operand with the Register n.

CMP Rn, <operand>

B - Branch

This will always branch to the instruction at position <label> in the program.

B <label>

BEQ - Branch If Equal

This must follow a CMP, and if the CMP values are equal this OpCode will branch to the specified <label>

BEQ <label>

BNE - Branch If Not Equal

This must follow a CMP, and if the CMP values are not equal this OpCode will branch to the specified <label>

BNE <label>

BGT - Branch If Greater Than

This must follow a CMP, and if the CMP values are Greater Than this OpCode will branch to the specified <label>

BGT <label>

BLT - Branch If Less Than

This must follow a CMP, and if the CMP values are Less Than this OpCode will branch to the specified <label>

BLT <label>

AND - Bitwise And

This OpCode will perform a bitwise logical AND between the values in Register n and the <operand>.

This will compare both inputs, it will output a 1 for each bit when both inputs are a 1. All other outputs will be a 0

The result is stored in Register d

AND Rd, Rn, <operand>

ORR - Bitwise Or

This OpCode will perform a bitwise logical OR between the values in Register n and the <operand>.

This will compare both inputs, it will output a 1 for each bit when either inputs are a 1. All other outputs will be a 0

The result is stored in Register d

ORR Rd, Rn, <operand>

EOR - Bitwise Xor

This OpCode will perform a bitwise logical XOR between the values in Register n and the <operand>.

This will compare both inputs, it will output a 1 for each bit when either but not both inputs are a 1. All other outputs will be a 0

The result is stored in Register d

EOR Rd, Rn, <operand>

MVN - Bitwise Not

This OpCode will perform a bitwise logical NOT between the value in the <operand>.

This will negate the input by swapping all 1's for 0's, and 0's for 1's

The result is stored in Register d

MVN Rd, <operand>

LSL - Logical Shift Left

Logically shift left the value stored in Register n by the number of bits specified by the <operand>.

The result is stored in Register d

Logical shifts can be useful as efficient ways to perform multiplication or division of unsigned integers by powers of two. Shifting left by n bits on a signed or unsigned binary number has the effect of multiplying it by 2_n.

LSL Rd, Rn, <operand>

LSR - Logical Shift Right

Logically shift right the value stored in Register n by the number of bits specified by the <operand>.

The result is stored in Register d

Logical shifts can be useful as efficient ways to perform multiplication or division of unsigned integers by powers of two. Shifting right by n bits on an unsigned binary number has the effect of dividing it by 2_n (rounding towards 0).

LSR Rd, Rn, <operand>

HLT - Halt Program

Causes the processor to stop executing your program.

HLT