Computer Architecture and Microprocessors

ByNavdeep Goyal

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

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

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

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

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

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

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

OPCODES

• LDA 0000• ADD 0001• SUB 0010• OUT 1100• HLT 1111

OPCODES AND OPERAND

Complete code includes opcode and operand

Like LDA 04H0000 0100

One instruction is executed in one instruction cycle

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

Ring Counter

SAP-1

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

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 1T3 0 0 1 1 0 1 1 0 0 0 1 1

Control Words for various instructions

Control Unit of SAP-1

Microprogrammed Control Unit

• Easier to fabricate• Slower-not useful for commercial

microprocessors• Can be used for testing various instructions

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

8085 Pin Diagram

Architecture of 8085

Thanks