Algorithm of second pass of Assembler

Algorithm of Second pass of assembler


Step 1: Set Location Counter to beginning

Step 2: Scan next line of code, if pseudo instruction present then go to step 3, else go to step 8.

Step 3:Check whether origin present , if yes then go to step 4, else go to step 5

Step 4: Set Location Counter and go to Step 2.

Step 5: Check whether end occur if yes then go to last step 17 ,else go to step 6.

Step 6:Convert operand to binary and store in location given by LC.

Step 7:Increment LC and go to step 2.

Step 8:Check whether Memory Reference Instruction or not , if yes then go to Step 9, else go to Step 13.

Step 9: Get operand code and set 2 -4 bits of instruction format.

Step 10:Search address symbol table for binary equivalent of symbolic address and set bits 5 – 16 of instruction format.

Step 11: Check the mode , I is present of not, if present then set first bit to 1, else set first bit to 0.

Step 12: Assembly all parts of binary instruction and store in location given by LC, and go to step 7.

Step 13:Check whether valid NON-MRI instruction or not, if valid then go to next , else go to step 16.

Step 14: Store binary equivalent of instruction in location given by LC.

Step 15:Go to step 7.

Step 16: Error in Code , and go to step 7.

Step 17: done , Stop