this is document about assembler directives and it has almost all the assembler directives
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This is Assembler Pass1 and Pass2 Algorithm
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Ex no 2
IMPLEMENTATION OF OF PASS1 OF THE TWO PASS ASSEMBLER
AIM: To implement a PASS 1 of a two pass assembler, using C language. ALGORITHM: Step 1: Read the input line.
op code field in the input line is “START”. Step 2: Check to see if the opcode 1. Find if if there is is any operand operand field field after after START; START; initia initialize lize the the LOCCTR LOCCTR to the operand value. 2. Otherwise Otherwise if if there is is no value value in the the operand operand field field LOCCTR is set to zero. Step 3: Write the line to the intermediate file. Step 4: Repeat the following for the other lines in the program until the opcode field contains end directive.
1. If there is a symbol in the label field. a. Check the symbol table to see is=f has already been stored over there. If so then it is a duplicate symbol, the error message should be displayed. b. Other wise the symbol is entered into the SYMTAB, along with the memory address in which it is stored. 2. If there is an opcode in the opcode field d. Search the OPTAB to see if the opcode is present, if so increment the location counter (LOCCTR) by three. e. i. If the opcode is WORD, increment the LOCCTR by three. ii. If the opcode is is BYTE, increment increment the LOCCTR by one. iii. iii. If the opcode opcode is RESW, incremen incrementt the LOCCTR LOCCTR by integer integer equivalent of the operand value *3. iv. If the opcode is RESB, increment the LOCCTR by the integer equivalent of the operand value. 3. Write each and every line processed to the intermediate file along with the location counters. Step 5: Calculate the length of the program by subtracting the starting address of program from the final value of the LOCCTR. Step 6: Close all the opened files and exit.
