Assembly Language
Contents
- 1 Example Programs
- 2 Operands
- 3 Op Codes
- 3.1 LDR - Load
- 3.2 STR - Store
- 3.3 ADD - Add
- 3.4 SUB - Subtract
- 3.5 MOV - Move
- 3.6 CMP - Compare
- 3.7 B - Branch
- 3.8 BEQ - Branch If Equal
- 3.9 BNE - Branch If Not Equal
- 3.10 BGT - Branch If Greater Than
- 3.11 BLT - Branch If Less Than
- 3.12 AND - Bitwise And
- 3.13 ORR - Bitwise Or
- 3.14 EOR - Bitwise Xor
- 3.15 MVN - Bitwise Not
- 3.16 LSL - Logical Shift Left
- 3.17 LSR - Logical Shift Right
- 3.18 HLT - Halt Program
Example Programs
Assembly Language Multiplication
Assembly Language Check for ODD / EVEN
Assembly Language Twos Complement
Assembly Language Logical Shift
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 2n.
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 2n (rounding towards 0).
LSR Rd, Rn, <operand>
HLT - Halt Program
Causes the processor to stop executing your program.
HLT
