CHAPTER 10 INSTRUCTION SETS

1. CHAPTER 10 INSTRUCTION SETS CSNB123 coMPUTERoRGANIZATION Systems and Networking

2. Architecture Recap Chapter 1 • Attributes visible to the programmer • Instruction set • Number of bits used for data representation • I/O mechanisms • Addressing techniques Systems and Networking

3. Machine Instruction Characteristics • Each instruction must contain the information required by the processor for execution Systems and Networking

4. Machine Instruction Characteristics (Cont.) • Elements of Machine Instruction (MI) Systems and Networking

5. Simple Instruction Format • Instruction is represented by a sequence of bits • During instruction execution, an instruction is read into an instruction register (IR) in the processor. • The processor must be able to extract the data from the various instruction fields to perform the required operation • Opcodes are presented by abbreviations-mnemonics-that indicate the operation ..why do this …hard to remember code in binary form Systems and Networking

6. Simple Instruction Format (Cont.) • Operands also represented symbolically • Example: • Add the value contained in the location Y to the contents of register R • Y=refer to the address of a location in memory • R=refers to a particular register ADD R,Y Systems and Networking

7. Instruction Types • HLL language instruction in BASIC • Instruct the computer to add the value stored in Y to the value stored in X and put the result in X. X=513, Y=514 X=X + Y Systems and Networking

8. Instruction Types (Cont.) X=513, Y=514 X=X + Y Simple instruction sets • Load a register with the contents of memory location 513 • Add the contents of memory location 514 to the register • Store the contents of the register in memory location 513 Systems and Networking

9. Instruction Types (Cont.) Systems and Networking

10. Number of Address • Address refer to location that store the value of the operands • In most architecture, most instructions have 1,2 or 3 operand addresses Systems and Networking

11. Example Y=(A-B)/[C+(DXE)] Systems and Networking

12. 3 address instructions • Each instruction specifies two source operand locations and a destination operation location • Operand 1, Operand 2, Result • Not common since they require a relatively long instructions format to hold the three address references • T = temporary location-to store intermediary result Systems and Networking

13. Example Y=(A-B)/[C+(DXE)] Systems and Networking

14. 2 address instructions • Each instruction specifies both an operand and the result location • Operand 1, Operand 2, Result • MOVE – is used to move one of the values to a result/temp loc before performing the operation • Reduce space for address Systems and Networking

15. Example Y=(A-B)/[C+(DXE)] Systems and Networking

16. 1address instructions • Second address must be implicit (hidden) • Common in earlier machines- the implied address being a processor register known as the accumulator (AC) • The AC contains one of the operands and is used to store the result Systems and Networking

17. Example Y=(A-B)/[C+(DXE)] Systems and Networking

18. 0 address instructions • All address must be implicit (hidden) • Stack-based operations • last-in-first-out (LIFO) set of locations • Interact with the stack using PUSH and POP operations • PUSH – to push a data from memory onto the stack • POP – to pop out data from the stack to a memory location Systems and Networking

19. Example Y=(A-B)/[C+(DXE)] D B C C A A A A A PUSH B PUSH A SUB PUSH D PUSH C E D D C C C PUSH E ADD DIV A A MPY A A POP Systems and Networking

20. Number of Address (Cont.) • Fewer address • require less complex processor • Instruction become shorter • But contain more total instructions-longer execution time Systems and Networking

21. Number of Address (Cont.) • Multiple address instructions – have multiple general purpose register • Register references are faster than memory references – speed up the execution • Most contemporary machine employ a mixture of 2 and 3 address instructions Systems and Networking

22. Types of Operands • Categories of data • Addresses • Numbers • Integer/floating point • Characters • ASCII etc. • Logical data • 0/1-false/true Systems and Networking

23. Types of Operations • Data transfer • Arithmetic • Logical • Conversion • I/O • Transfer of control Refer to Table 9.3 Systems and Networking

24. Types of Operations (Cont.) Systems and Networking

25. Types of Operations (Cont.) Systems and Networking

26. Control Operations • Branch/jump instruction • Sequential • Unconditional branch • Conditional branch • Skip • Subroutine / procedure call Systems and Networking

27. Control Operations - Branch • Has one of its operands the address of the next instruction to be executed • A sequence of code in a computer program which is conditionally executed depending on whether the flow of control is altered or not (at the branching point) • Conditional – the branch is made only if a certain condition is met • Unconditional – a branch instruction in which the branch is always taken Systems and Networking

28. Control Operations - Branch (Cont.) Systems and Networking

29. Control Operations - Skip • Useful in loop control • Implies that next instruction to be skipped Systems and Networking

30. Control Operations – Subroutine • Also known as procedure call • A self-contained computer program that is incorporated into a larger program • At any point in the program, the procedure may be called or invoked • The processor is instructed to go and execute the entire procedure and then return to the point from which the call took place • A procedure allow the same piece of code to be used many times • Involves two basic instructions; call and return instruction Systems and Networking

31. Control Operations – Subroutine (Cont.) Call instruction Return instruction Instruction that returns from the procedure to the place from which it was called • Instructions that branches from the present location to the procedure Systems and Networking

32. Control Operations – Subroutine (Cont.) Systems and Networking