COURSE OUTCOMES OF Microprocessor and programming Describe the architecture and organization of microprocessor along with instruction set format. C404.2 Describe modes and functional block diagram of 8086 along with pins and their functions C404.3 List and describe memory and addressing modes C404.4 List, describe and use different types of instructions, directives and interrupts C404.5 Develop assembly language programs using various programming tools. Visit for more Learning Resources

C404.1 Describe the architecture and organization of microprocessor along with instruction set format. C404.2 Describe modes and functional block diagram of 8086 along with pins and their functions C404.3 List and describe memory and addressing modes C404.4 List, describe and use different types of instructions, directives and interrupts C404.5 Develop assembly language programs using various programming tools.

Chapter 2 16 BIT MICROPROCESSOR 8086

Features of 8086 microprocessor 16 bit microprocessor 20 address lines i.e 2^20=1MB memory addressed. 16 bit address and data bus multiplexed i.e AD0-AD7 to minimize no of pin on IC Clock frequency between 5Mhz-10Mhz Arithmetic operation on 8 bit or 16 bit signed or unsigned data including multiplication 7 division. Operate in single processor or multiprocessor Instruction set-> powerful->flexible. 256 interrupt Operate in max& min mode to achieve high performance Support multiprogramming Separate instruction set for string manipulation.

Architecture of 8086 microprocessor

Architecture of 8086 It is divided into 2 parts 1) Bus interface unit (BIU) 2) Execution unit (EU) Bus Interface unit := It acts as interface between system bus and the execution unit. Fetches instruction from memory. Reads data from I/O ports and memories. Writes data to ports and memories Supports pipelining. BIU handles transfer of data on all the buses for the execution unit. Blocks of BIU:= Queue= To speed up the program execution BIU fetches as many as 6 instruction bytes from memory . These pre-fetched instruction byte for execution unit in FIFO group of registers called a QUEUE.

Concept of pipelining:= fetching the next instruction while recent instruction executes is known as pipelining. 6 5 4 3 2 1 I1 I2 I3 I4 I5 I6 I7 I8 I9 1 2 3 4 5 6 7 8 9 Clock cycle F I1 I2 I3 I4 I5 F-Fetch D I1 I2 I3 I4 D-Decode E-Executes E I1 I2 I3 Clock cycle Fig: pipelined execution of 3 instruction 1 2 3 4 5

On non pipelined processor 9 clock cycle are required for individual fetch , decode & execute for 3 instruction. On pipelined processor fetch, decode & execute operation are performed in parallel. -only 5 cycle are required to execute 3 instruction. - 1 instruction requires -> 3 cycle to completes. Additional instruction complete at rate of one per cycle. During clock cycle 5 I3 instruction executing , I4 is decoding , I5 instruction fetched. If 1000 instruction it requires 3000 clock cycle on non pipelined processor.----> require 1002 clock cycle on pipelined processor. In 8086 performs fetch , decode , & executes instruction in parallel.

The BIU contain 4 16 bit segment registers it hold upper 16 bit of starting address of 4 memory segment that 8086 is working with particular time . Es hold upper 16 bits of starting address of extra segment Cs hold upper 16 bits of starting address of code segment Ss & Ds hold upper 16 bit of starting address of stack segment & data segment. ES Segment Register CS SS DS Instruction pointer IP 3) Instruction Pointer Register (IP) := - Ip register hold 16 bit address of next code byte within code segment . It contain offset from base address to next instruction byte to be fetched

Execution Unit The execution unit of 8086 informs BIU of address of instruction & data needed for execution &execute it.

Functional block of EU 1) Control circuit ,instruction decoder , ALU The execution unit contain control circuit that direct all internal operation. The execution unit has 16 bit ALU block that perform arithmetic & logical operation like +, - , *,AND , OR ,NOT The instruction decoder in EU that translates the instruction fetch from memory into a series of action that EU carried out.

8086/88 internal registers 16 bits (2 bytes each) AX, BX, CX and DX are two bytes wide and each byte can be accessed separately These registers are used as memory pointers. Flags will be discussed later Segment registers are used as base address for a segment in the 1 M byte of memory

-The execution unit has 8 general purpose register labeled as AH,AL,BH,BL,CH,CL,DH,DL These register can be used for temporary storage of 8 bit data & 16 bit data AH-AL pair is referred as AX , BH- BL pair is referred as BX , CH-CL pair is referred as CX , DH-DL pair is referred as DX. 1) Stack pointer register: It contain a 16 bit offset added to stack segment register indicates address of memory location when word was most recently stored. Base pointer register: The base pointer register can be used instead of stack pointer register to access memory location within the stack The 20 bit address can be obtained by shifting the contents of the stack segment by 4 bits & adding the contents of BP to it

3) Source index register: The source index register is used to load 16 bit offset of a data word in data segment . The physical address of the data word can be obtained by shifting the contents of DS register by 4 bits & adding into SI 4) Destination index register It is used to hold the 16 bit offset of a data word in extra segment while executing string instruction The 20 bit physical address is calculated from DS & DI

Multiplexed address & data pin Multiplexed address & status pins Select Minimum/ maximum mode Multplexed address and data bus Interrupt Pins

8086 operates into 2 modes 1) minimum mode 2) Maximum mode The following pins are important in both minimum & maximum mode CLK( pin no-19) The maximum clock frequency 5-10MHZ Provides basics timing for processor & bus controller. It is symmetric square wave with 33% duty cycle. 2) Vcc (pin no-40) Provide +5v power supply pin 3) GND (pin no-1,20) Ground for internal circuit

4) RESET (pin no-21) It is a system reset When this signal goes high ,processor enter into reset state &terminate the current activity & start execution from FFFF0H Active high signal - for at least 4 clock cycle. 5) AD0-AD15 These lines are multiplexed ,bi-directional address / data bus 8086 has 20 bit address bus( A0-A19) 16 bit data bus During t1 cycle  carry lower order 16 bit address T2,t3,t4 - carry 16 bit data So AD0-AD7 lines carry lower order byte of data& AD8 –AD15 carry high order byte of data

6) A19/s6 , A18/s5 , A17/s4 , A16/s3 These lines are multiplexed address & status lines Upper 4 bits address sent on this lines for memory operation During I/O operation these lines are low During memory & I/O operation status information is availble on these lines in T2,T4 cycles. status of interrupt flag indicated by S5 S4 S3 segment Register 0 0 alternate data 0 1 stack 1 0 code 1 1 Data 7) BHE /S7 (pin no- 34) - bus high enable / status During t1 state BHE signal is used to enable dat on most signficant half of data bus pins D15- D8..S7 status information availble during t2,t3,t4 status - remain high

BHE A0 word /byte access 0 0 whole word from even address 0 1 upper byte from / to odd address 1 0 lower byte from / to even address 1 1 none 8) RD (pin no-32) Active low signal Read strobe indicates that processor is performed memory, I/O read cycle depending on s2 pin 9) Ready (pin no-22) When high-- carry out it normal operation When low - freezes it’s bus & enters a wait state -

10) INTR (pin no-18) Interrupt request High level triggered interrupt request i/p Checked last clock to check availability of request If request is not occurred ,processor enters interrupt acknowledge cycle 11) TEST (pin no-23) This i/p is examined by 8086 wait instruction If TEST i/p  low - execution continued -- if not then processor enter /wait in idle state 12) NMI (pin no-17) Non mask able interrupt NMI is not mask able internally by software A transition from low- high initiates the interrupt at the end of current instruction It is edge triggered i/p interrupt causes type-2 interrupt

MN / MX Pin indicates the operating mode of 8086 There are 2 modes of OS i.e maximum and minimum modes MN/MX - high 8086 operating in -- minimum mode MN/MX - low 8086 operating in -- maximum mode

Signal description pins for minimum mode := M/IO (pin no-28) status line:- This signal is used to distinguish between memory access & I/O access 2) WR (pin no-29) Write:- This signal indicates that processor is performing a memory write depending on the state of M/IO signal 3) INTA (pin no-24) interrupt acknowledge -used as an active low interrupt acknowledge signal It is used as a read strobe for interrupt acknowledge cycle 4) ALE (pin no-25) address latch enable - High  8086 indicates ADDR1 DATA & ADDR/STATUS bus High pulse active - during t1 state of bus cycle 5) DT /R (pin no-27) data transmit/receive -these signal used to decide direction of data flow through the transceivers 8286/8287

-processor send data out -- signal high Processor receives data --- signal low 6) DEN (pin no-26) data enable - Signal provides an output enables signal for transceivers 8286 / 8287 7) HOLD Active high i/p signal 8) HLDA - Active high o/p signal

* Signal description of pins for maximum mode:= Qs1 ,Qs0 (pin no-24,25) queue status Qs1 Qs0 features 0 0 no operation 0 1 first byte of opcode from queue 1 0 empty the queue 1 1 subsequent byte from queue LOCK (pin no-24) Active low signals indicates that other system bus masters are not to gain control of system while lock is active low. lock is activated by lock prefix instruction & remain active until completion of next instruction.

Interrupt Acknowledge 1 I/O read I/O write Halt Op-code Fetch 3) S0, S1, S2 - Are status lines which indicate the type of operation, being carried out by processor. S2 S1 S0 Status Interrupt Acknowledge 1 I/O read I/O write Halt Op-code Fetch Memory Read Memory Write Passive

4) RQ/GT0, RQ/GT1 (Request/Grant) Are used by other local bus masters, in max mode, to force the processor to release the local bus at the end of the processor’s current bus cycle.

Memory Address Generation Intel Memory Address Generation The BIU has a dedicated adder for determining physical memory addresses Offset Value (16 bits) Segment Register (16 bits) 0 0 0 0 Adder Physical Address (20 Bits)

Byte Top of Stack end of code segment 6FFFF SP = FFE0 6FFE0 H Physical address 0123 Start of stack segment 60000 H SS: 60000 + SP: FFE0 = Physical address 6FFE0 Physical Address generation for stack segment

8284 Pin Diagram:

8284 Block Diagram: x1 AEN1 CSYNC F / C Clock OSC Clock Logic x2 EF1 PCLK RDY1 AEN1 Ready Logic READY RDY2 AEN2 Reset Logic RESET RES

8086 System Minimum mode (74LS373) (74LS245)

Processor Timing Diagram of 8086 (Minimum Mode) for Memory or I/O Read CLOCK __ DT/R ALE AD15 - AD0 A15 - A0 D0 – D15 (from memory) A19/S6 - A16/S3 A19 - A16 S6 - S3 __ IO/M if I/O ACCESS this is HIGH, if MEMORY ACCESS this is LOW ____ RD ______ DEN

Processor Timing Diagram of 8086 (Minimum Mode) for Memory or I/O Write CLOCK __ DT/R ALE AD15 - AD0 A15 - A0 D15 - D0 (from memory) A19/S6 - A16/S3 A19 - A16 S6 - S3 __ IO/M if I/O ACCESS this is HIGH, if MEMORY ACCESS this is LOW ____ WR ______ DEN

8086 System Maximum Mode

Processor Timing Diagram of 8086(Maximum Mode) for Memory or I/O Read CLOCK __ DT/R ALE D0-D15 AD15- AD0 A15 - A0 S2-S0 S2-S0 Active S2-S0 Inacive A19/S6 - A16/S3 A19 - A16 S6 - S3 MDRC/IORC ______ DEN

Processor Timing Diagram of 8086(Maximum Mode) for Memory or I/O Write CLOCK __ DT/R ALE D0-D15 AD15- AD0 A15 - A0 S2-S0 S2-S0 Active S2-S0 Inacive A19/S6 - A16/S3 A19 - A16 S6 - S3 MWTC &IOWC AMWC/AIOWC ______ DEN For more detail contact us