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General Format of an instruction

/*
Comments
*/

Label : Opcode operands ; //Comments

Token What Usage
Label Any Valid Variable name Used to mark an instruction as well as Data.Instruction may or may not contain Label. Compulsary to mark an instruction when using Branching Operation. ALSO , when declaring a variable Label should clearly be DATA OR when assigning value to a variable , Label must be DATA. SEE : Labels
: To be used after Label. To be used even if there is no Label Tells the assembler about end of label. Every Instruction must use : Throws an error otherwise
Opcode The string representing instruction. Must be from the list given below. If not , throw an error
Operands Operands to be used with Opcode. Must be defined in this procedure , Variable name should be valid , Number of operands must be equal to those demanded by Opcode
; End of Instruction Compulsary to use in every instruction. if : is reached directly after ; Or file ends and ; is not present , then throw error.
\\ Single line comments Everything after ; is ignored as long as it is in same line
/* Comments */ Multi-line comments Everything in between /* and */ is ignored. Throw error if either of two is missing

Labels

Labels are of two types :

Variable Types What
ADDRESS Represents an address. Defined as Label
DATA Represents Data eg. 2,5,16 etc., Declared explicitly

DATA is a reserved keyword. Whenever defining a variable the label must clearly be DATA.
General Format DATA : type variable name , value ;
Eamples :
>> DATA : int y , 10 ; //variable y declared and assigned value 10
>> DATA : int y ; //variable y declared but not assigned any value.
>> DATA : y = 10 ; //Already assigned vaiable attached a value.

ADDRESS is not a keyword. Any valid variable name can be used to mark address of an instruction
Examples :
>> Addition : Add x ; //Labeled Addition
>> : BRZ Addition ; // No label to it. But can jump to "Address"

VALID VARIABLE NAME :

  1. Can contain English alphabets , digits 0-9 and only one special character _.
  2. Cannot Start with a digit.
  3. Cannot contain tabs , spaces new line etc.

Possible Errors

1)Variable name not valid
2)Variable is already declared

Opcodes

Opcode Assembly Opcode Parameters Meaning
0000 CLA - Clear accumulator
0001 LAC x Load into accumulator from address
0010 SAC x Store accumulator contents into address
0011 ADD x Add address contents to accumulator contents
0100 SUB x Subtract address contents from accumulator contents
0101 BRZ ADDRESS Branch to address if accumulator contains zero
0110 BRN ADDRESS Branch to address if accumulator contains negative value
0111 BRP ADDRESS Branch to address if accumulator contains positive value
1000 INP x Read from terminal and put in address
1001 DSP x Display value in address on terminal
1010 MUL x Multiply accumulator contents and address contents
1011 DIV x , R1 , R2 Divide accumulator contents by **address content **. Quotient in R1 and remainder in R2
1100 STP - Stop execution
Assemble Opcode Possible Errors
CLA -
LAC x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable
SAC x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable, Accumulator Contents Not Set
ADD x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable, Accumulator Contents Not Set
SUB x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable, Accumulator Contents Not Set
BRZ ADDRESS Variable not defined , **Variable Type : ADDRESS expected **
BRN ADDRESS Variable not defined , **Variable Type : ADDRESS expected **
BRP ADDRESS Variable not defined , **Variable Type : ADDRESS expected **
INP x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable
DSP x Variable not defined , **Variable Type : DATA expected ** , Value not assigned to variable
MUL x Value not defined ,**Variable Type : DATA expected ** , Value not assigned to variable , , Accumulator Contents Not Set
DIV x , R1 , R2 Variable not defined , Zero division error , Variable Type : DATA expected , Value not assigned to variable , Accumulator Contents Not Set
STP If anything after STP , Not reachable Code

Errors Defined

     
(1) typeMismatchError :          
        (i) `DATA` expected and `ADDRESS` passed and ice-versa.                
        (ii) In `ADD`,`MUL`,`SUB`,`DIV` Type of opperand different from accumulator type.         
        (iii) Variable defied type `A` and found to be type `B`.         
        
(2) variableError :         
        (i) Variable name invalid.     
        (ii) Variable not defined.     
              (a) `ADDRESS` not defined,     
              (b) `DATA` not defined,     
        (iii) Value not assigned.      

(3) syntaxError :     
        (i)`:` missing.      
        (ii) `;` missing.     
        (iii) Opcode invalid.    
        (iv) Possible variable defination , but not labelled `DATA`     
        (v) Multiline comment :   
            (a) Not starting , but ending.     
            (b) Not ending but start found.
            
(4) mathEror :       
    (i)zeroDivisionError

(5) accumulatorContentsNotSetError : Thrown when during program , accumulator is not cleared or No data is loaded. But an operation is done using contents of accumulator.