Computer Architecture and Microprocessors

1. Computer Architecture and Microprocessors By Navdeep Goyal

2. Purpose of Talk • What are the advantages of teaching these topics to physics students • To discuss the curriculum for teaching microprocessors to physics students • Introduction to SAP-1 • 8085 microprocessor

3. Importance . Learning about the design considerations of microprocessors is important . Students opting for further studies in microelectronics are benefitted . Knowledge of working of a processors is important . Starting with working of simplest computer system is always helpful . Better to start with few basic principles of working of computer systems

4. Proposed Sequence • Which device was designed first • Computer or microprocessor? • Bus organised computer systems • Data Bus • Address Bus • Control Bus • Tri-state Devices • Buffer Registers • SAP-1, SAP-2 etc • 8085 microprocessor • 8086 and other advanced microprocessors

5. BUS SYSTEM • In all computer system, the data is transferred from one place to other through common DATA BUS • The selection of device is from the address, which is sent through common address bus • Depending upon control signals data is written onto or read from a particular register

6. TRI STATE DEVICES • TRI-STATE Devices play important role when we are dealing with bus organized computer systems • Three terminal device: • Input, output, control • Available in high active or low active mode • Used at the output of registers, which are connected with common data bus

7. Buffer Registers • The loading of data and reading data from buffer register is with the help of control signals • For loading data onto register a Load (L) signal is used • For receiving data from buffer register an Enable (E) signal is used • For different registers loading or enabling may be high or low active

8. Introduction to Sap-1 • SAP-1 stands for simple as possible computer • SAP-1 is a computer made from discrete IC’s • Its an 8 bit computer with 4 address lines • Can handle max. of 16 address locations • Instruction set includes instructions • LDA, ADD, SUB, OUT, HLT

9. OPCODES • LDA 0000 • ADD 0001 • SUB 0010 • OUT 1100 • HLT 1111

10. OPCODES AND OPERAND Complete code includes opcode and operand Like LDA 04H 0000 0100 One instruction is executed in one instruction cycle

11. Machine Cycle/Instruction Cycle • Instruction cycle may consist of many machine cycles • For SAP-1, Instruction cycle= machine cycle • Instruction cycle=Fetch cycle+Execution Cycle • Fetch cycle is generally same for all instructions

12. Ring Counter

13. SAP-1

14. How to fabricate various units • Program Counter: 4 bit counter-made from J-K flip-flops-74 LS107 with 74LS126 • Input/MAR: includes address/data switch registers includes buffer register and 2-1 multiplexer • 16X8 RAM • Instruction Register: 8 bit buffer register , 2 nos 74 LS173 • Controller Sequencer: to generate control signals • Accumulator: Buffer register to store intermediate results • Adder Subtracter: Arithmatic unit • B: buffer register

15. Control Signals Fetch T1 0 1 0 1 1 1 1 0 0 0 1 1 T2 1 0 1 1 1 1 1 0 0 0 1 1 T3 0 0 1 1 0 1 1 0 0 0 1 1

16. Control Words for various instructions

17. Control Unit of SAP-1

18. Microprogrammed Control Unit • Easier to fabricate • Slower-not useful for commercial microprocessors • Can be used for testing various instructions

19. Variable Machine Cycle • Fixed machine cycle may give many unwanted time states • Execution is going to take longer time • Better to opt for variable machine cycle

20. 8085 Pin Diagram

21. Architecture of 8085

25. Thanks