ICS 331: System Software (981)

Quiz # 2

Date: October 6, 1998                                                                                                Time: 20 minutes

Question 1:

List two of the major functions that are performed by an assembler in pass 2.                                (3 Points)

1) Replace all mnemonics by op code and all symbols of operands by addresses/displacements.

2) Assemble the instructions and produce the object code and program listing.

Question 2:

Generate the value of LOC and the object code of the following SIC/XE assembly program:       (14 Points)

 

Line

LOC

Sources Statements

Object Code

1

1055

   QUIZZ

START

1055

2

1055

   FIRST

+LDB

#4096

69101000

3

1059

LDA

X'454F46'

032006

4

105C

STA

RESULT

0F2000

5

105F

   RESULT

RESW 

1

6

END

 QUIZZ

7

1062

  *

=X'454F46'

454F46

 

You may need the following information: (Op Code for LDA is 00, for LDB is 68, and for STA is 0C.
The order of Flags Bits is: n-i-x-b-p-e.)

Question 3:

Briefly describe how does the assembler indicate to the loader that an assembly program may need some
changes in its object code before loading it into the memory.                                                     (3 Points)

It creates a modification record for every statement that needs to be changed during loading time,
which are extended format instructions. The change is done by adding the Loading address of the
program to this address. The record contains the address and the length of the part to be modified.