Algorithm of Pass1 Assembler In System Programming.

Algorithm of Pass1 Assembler

Step1:- Start

Step2:- Set Location Counter (LC)=0

Step3:- Read Card   [Read1]

Step4:- If Pseudo-opcode is Present [POTGET1]

            Then Go to step 5.

            Else

a)      Search Machine-opcode [MOTGET]

b)      Set L <- Length

c)      Process any literal, enter into literal table[LTSTO]

d)     Go to step6

Step5:- While (P-opcode !=END)                  //P-opcode means Pseudo-Opcode

            do

If(P–opcode ==DS || P-opcode ==DC)

Then

a)      Adjust LC to proper Alignment.

b)      Set L= Length of data field

c)      Go to Step 6

Else If(P-opcode == EQU) then

a)      Evaluate operand field (EVAL)

b)      Assign the value to symbol in label field[STSTO]

c)      Go to step 7

Else

a)      Go to step 7 and save the Using and Drop cards for pass 2.

End While

Step 6:- If(any symbol) then

a)      Assign current value of LC to symbol

b)      Set LC= LC+L

Else

a)      Set LC=LC+L

Step 7:- Write copy of card on file for use by pass 2 [Write 1] and Go to step3. Repeat this step (Go to step3) until all instructions are not processed.

Step 8:- If (P-opcode ==End)

               Then

a)      Assign storage location to literals [LITASS].

b)      Rewind and reset copy file.

c)      Move to Pass2.

Step 9:- Exit.