1. 1 Programming in Machine Language SCSC 311 Spring 2011

2. 2 Index  Overview  Bit-wise Logical Operations

3. 3 Brookshear Machine Architecture

4. 4 16 general-purpose registers numbered 0 through 15 Hex notation: numbered 0 through F 256 byte-size main memory cells (i.e., 8 bits each) numbered 0 through 255 Hex notation: numbered 00 through FF 12 simple instructions encoded using 16 bits (2 bytes) per instruction Hex notation: 4 hex digits per instruction  One hex digit for op-code  Other three hex digits for Operands

5. 5 Instruction Format 0011 0101 1010 0111 16-bit patterns per instruction 35A7 Hex form Operand Op-code

6. 6 0iii - No-operation 1RXY - Load register R with contents of location XY 2RXY - Load register R with value XY 3RXY - Store contents of register R at location XY 4iRS - Move contents of register R to register S 5RST - Add contents of registers S and T as binary numbers, place result in register R 6RST - Add contents of registers S and T as floating-point numbers, place result in register R 7RST - OR together the contents of registers S and T, place result in register R 8RST - AND together the contents of registers S and T, place result in register R 9RST - XOR together the contents of registers S and T, place result in register R ARiZ - Rotate the contents of register R one bit to the right, Z times BRXY - Jump to instruction at XY if contents of register R equal contents of register 0 Ciii - Halt DRXY - Jump to instruction at XY if contents of register R are greater than contents of register 0 R,S,T - Register numbers XY - A one-byte address or data value Z - A half-byte value i - Ignored when the instruction is de-coded: usually entered as 0

7. 7 GUI: three major sections  the PC registers contain working data values as well as the Program Counter  the Memory contains hexadecimal encoded instructions and data;  the Run controls on the bottom, control the start, stop and speed of the simulation as well as allowing the user to reset the PC registers and Program Counter.

8. 8

9. 9 Example: Trace a program by hand Trace the following machine instruction by hand and write the results, given the contents of main memory as in the table AddressContents 0015 016c 0216 036d 0450 0556 0630 076e 08c0 0900 6a 6b 6c0b 6d0c 6e

10. 10 Index  Overview  Bit-wise Logical Operations

11. 11 Bit-wise Logical Operations  A byte can be seen as a set of 8 Boolean variables each bit is one variable  Logical instructions like AND, OR, XOR, etc. performed by aligning the bytes and performing the logical operations on the corresponding bits, one by one.

12. 12 Bit-wise Logical Operations ANDOR 100100111100001 111000110001100 100000111101101 XOR 100101001 111001101 011100100

13. 13 Masking  Goal: To test the individual pattern of bits in a given string of bits The sequence of bits that are used to examine a particular bit is known as the mask Using Mask, along with the appropriate logical operation, a programmer can determine the values of individual bits in a byte

14. 14 Masking Technique 1: Reading  Reading a bit in a bit string is done by masking away the bits we are not interested in: AND operator along with a bit mask of 1 in the position we want to read  leave the interesting bit and mask away the others Example: Suppose you want to determine if a number is odd or even.

15. 15 Example  The low-order bit (rightmost binary digit) is 1 in an odd number and 0 in an even number.  A mask of …0001 with AND operator will test the last bit Even NumberOdd Number 1001010101010100101 AND 000000001AND0000000001 0000000000000000001 By examining the result of the masking operation, you can determine the number as odd or even: If the result is 0, it is even

16. 16 Exercise 1  Suppose you have an 8-bit string (a byte) that is in 2’s complement notation, sitting in a memory cell. You want to determine if it represents a positive or negative number. What bit-mask would you use? What Logical operation would you use?

17. 17 Masking Technique 2: Setting  Setting (set to 1) a bit in a bit string is done by an OR operation with 1 in the position we want to set to 1, 0 in the other positions leaving the other bits unchanged.  Example: Suppose you want to set the high-order bit to a 1 in a given bit string 00100110 OR 10000000 10100110

18. 18 Exercise 2  Suppose you want to set the 2 nd bit from left in a given bit string to 1. What is the bit mask you would use? and what is the operation to achieve the result? i.e., given the bit string 10000010, we want the result to be 11000010.

19. 19 Masking Technique 3: Re-Setting  Re-Setting (set to 0) a bit in a bit string AND with 0 in the bit position that needs resetting 1 in the other positions in order not to change the other bits  Example: Suppose you want to reset the high-order bit to a 0 in a given bit string 10100110 AND 01111111 00100110

20. 20 Exercise 3: Converting ASCII Case  Task: Develop a mask and select operator to convert uppercase ASCII characters to lowercase, e.g. “A” to “a”, “B” to “b”, etc.  Product: Mask and operator. (See ASCII code at next page )

21. 21 A0100 0001 B0100 0010 C0100 0011 D0100 E0100 0101 F0100 0110 G0100 0111 H0100 1000 I0100 1001 J0100 1010 K0100 1011 L0100 1100 M0100 1101 N0100 1110 O0100 1111 P0101 0000 Q0101 0001 R0101 0010 S0101 0011 T0101 0100 U0101 V0101 0110 W0101 0111 X0101 1000 Y0101 1001 Z0101 1010 a0110 0001 b0110 0010 c0110 0011 d0110 0100 e0110 0101 f0110 g0110 0111 h0110 1000 i0110 1001 j0110 1010 k0110 1011 l0110 1100 m0110 1101 n0110 1110 o0110 1111 p0111 0000 q0111 0001 r0111 0010 s0111 0011 t0111 0100 u0111 0101 v0111 0110 w0111 x0111 1000 y0111 1001 z0111 1010

22. 22 Exercise 4: Combining Nybbles A Nybble (or, nibble) is a half-byte = 4 bits  Task: You are given two bytes. You must create a third byte that combines the first half of the 1 st byte (4 bits) with the last half of the 2 nd byte (4 bits). For example, given 01101001 and 11100111, the answer would be 01100111. Devise a sequence of logical operations using bit masks to do this.

23. 23 Rotation: right and left “wrap around” Rotate left 1 position  01001010 10010100 Rotate left 1 position again  10010100 00101001 Rotate right 1 position  01001010 00100101 Rotate right 1 position again  00100101 10010010

24. 24 Shift: right and left  Shifting is similar to rotation, except the bits “fall off the end” instead of “wrap around”… and you “fill in” the gap with 0. Shift right 1 position  11001010  01100101 Shift right 1 position again  01100101  00110010 Shift left 1 position  11001010  10010100 Shift left 1 position again  10010100  00101000

25. 25 Arithmetic Shift  A special form of shift, except the sign bit is preserved Arithmetic shift to the right by one position 11001001  10100100

26. 26 Exercise 5: No Shift Instruction? (bonus)  The Brookshear machine does not have a SHIFT instruction, although there is a ROTATE  How can a SHIFT be accomplished in the Brookshear machine? Demonstrate your answer with two examples.

27. 27 Suppose the cell addresses 08-0F contain the following data: Address Contents 282A 293D 2A14 2BFF 2CF0 2DF1 2EF2 2FF3 Trace the following instructions and explain what the program does. 001128 021229 04132A 065412 085443 0A342A 0C4043 0E9413 10342B 12C000 What are the contents of cells 2A and 2B when program halts? Lab 2: Trace a program 1

28. 28 Lab 2: Trace a program 2  Run this program stored in cells 00 through 12 with different value in location 12: 04 02  What does this program do? Address: contents 00: 20 01: 00 02: 21 03: 01 04: 23 05: 01 06: 12 07: 12 08: B2 09: 10 0A: A1 0B: 07 0C: 50 0D: 03 0E: B0 0F: 08 10: C0 11: 00 12: 03

29. 29 Lab 2: Trace a program 3 (bonus) AddressContents 0010 0120 0211 0321 0422 0500 0626 0700 0823 0901 0A40 0B56 0C55 0D61 0E52 0F23 10B2 1114 12B0 130A 1435 1522 16C0 1700 AddressContents 2003 2102 2200 Try the following values in cells 20 and 21. In each case, write down the contents of cell 22 when the program completes execution. Case 1:cell 20 contains 04 and cell 21 contains 02 Case 2: cell 20 contains 05 and cell 21 contains 02 What does this program do?

30. 30 Lab 3: adding three numbers  Task: Write a program to add three numbers together. The numbers are stored at memory cell locations 10, 11, and 12. The result should be stored at location 13.

31. 31 Lab 3: Combining two Nybbles  Task: Develop a machine language program to combine two nybbles. combines the first half of the 1 st byte (4 bits) with the last half of the 2 nd byte (4 bits). The given two bytes are stored in locations 20 and 21, and the result byte should be stored in location 22.

32. 32 Lab 3: Write a BSML Program: ASCII case (bonus)  Task: Write a program to convert uppercase to lowercase for an ASCII character stored in a memory location 30