Microprocessor History

1. Microprocessor History

2. Early microprocessors • PMOS technology – slow and awkward to interface with TTL family • 4 bit processor • Instructions were executed in about 20 µs. • Intel 4004 the first MP. 4K nibbles address space. • Intel 8008- can manipulate a whole byte. • 16Kbytes address space • 50,000 operations/second.

3. N-channel MOSFET • 1970. • Faster than P-MOS. • Work with +ve supply; easy to interface with TTL. • 1973 Intel 8080 MP. • 500,000 operations/second. • 64K bytes memory. • Upward software compatible with 8008. • Other brands are MC6800, Fairchild’s F-8 etc.

4. Basic types of MP • Two types • Single component microprocessors • Bit sliced microprocessors • Can be cascaded to allow functioning systems with word size from 4 bits to 200 bits.

5. Single component M Computer • Composed of • A processor • read only memory (for program storage) • Read/Write memory (for data storage) • Input/output connections for interfacing • Timer as event counter • Intel 8048, Motorola 6805R2. • Oven, washing machine, dish washer etc.

6. Modern MP • 8, 16, 32, 64 bits are available. • Intel 8085, Motorola 6800 – 8 bit word 16 bit address. • Intel 8088, 8086, Motorola 68000 – 16 bits word, 20 bits address. • 80186 – never used. • 286 – real mode and protected mode; 16MB memory • 386 – paging, 4GB memory, 32 bits word • 486 – math coprocessor, L1 cache

7. Modern MP • Pentium • 64 bits i/o off the chip but process 32bits word, exception floating point processed 64 bits, cache doubled, instruction pipelining. • Pentium Pro • L2 cache, Improved pipelining • Pentium MMX • Multi-Media extensions, 57 new inter instruc mostly used for multimedia programming • Pentium II, III, IV • Pentium pro with MMX tech, increased L2 cache, full 64 bit operation • RISC • Reduced instruction set processor, uniform length instruc, faster in operation, cannot perform may different thing as CISC.

8. MP based system MP memory IO device

9. Basic MP architecture • Fetch, decode, execute. • PC increment. • First instruction is a fetch • 0000H for 8085 • FFFF0H for 8086, 8088 Data Bus AF, BC, DE, HL, SP, PC many more Register Array Instruction Register ALU Control Bus control Address Bus

10. Memory Interfacing and IO decoding

11. Interfacing needs bus • Isolation and separation of signals from different devices connected to MP. • Unidirectional • Bidirectional • LS373, 244

12. Memory map • Pictorial representation of the whole range of memory address space. • Defines which memory system is where, their sizes etc. • Address space or range. • 8086 has 1M address space in minimum mode. • 8085 has 64K address sspace.

13. Address Decoding • Address decoder is a digital ckt that indicates that a particular area of memory is being addressed, or pointed to, by the MP. • Absolute address decoding • Decode an address to one single output • Decode 10110 so that u can get a signal from the decoder when it receives exactly that bit pattern. • Partial address decoding • Some bits are used as don’t care so that decoder gives a signal for a range of consecutive bit patterns.

14. Absolute decoding 1 0 1 1 0 1 0 1 1 0 a b c d e Active low o/p signal a b c d e Can use decoder IC with gates to achieve exact decoded o/p 0 3 to 8 line dcd 1 0 1 o/p Logic 1 7 8 input NAND gate implementation

15. Partial decoding • When a range of addresses are deconded then it is called partial decoding. For example, if we need to generate a control signal for an address generated by the MP within the range FFF0 – FFFF, then it is called partial decoding. • Decoder, multiplexer can be used for address decoding A15 A14 1 1 1 1 1 1 1 1 1 1 1 1 x x x x A4

16. MEMR 8085 IO/M IOWR RD MEMWR WR IOWR Bus control signals

17. CE Interfacing A Memory Chip • 2K Byte memory • Memory address space of the chip: 8800H to 8FFFH A14 A15 IO/M A13 E1 E2 E3 3 to 8 decoder A12 MEMSEL Q1 A11 Memory Chip A10 D7 A9 D6 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 1 0 0 0 1 X X X X X X X X X X X A0 D0 RD 8 8 - F 0 - F 0 - F WR

18. Reading a byte from memory • Reading an Opcode 4Fh in memory location 2005H. • PC places the 16bit address 2005H of the memory location on the address bus. • Control unit sends the memory read signal (MEMR) to enable O/P buffer of the memory chip. • The value 4Fh stored in location 2005H is placed on the data bus and transferred to instruction decoder of the MP.

19. MUX W Temp Reg (8) Z Temp Reg (8) B (8) C (8) D (8) E (8) Reg Select H (8) L (8) Stack pointer (16) Program counter (16) Incrementer/decrementer Latch (16) 8085 functional block diagram External Add/data bus(8) Serial I/O control Interrupt control Temp Reg Accumu Instru Register (8) Instru Decoder Flags Address buffer (8) Data/Add buffer (8) Timing & control External Address bus(8)

20. MP operations • MP initiated Operations • Memory/IO read/write • Internal operations • Store 8-bit data • Arithmetic and logical operations • Test for conditions • Sequence the execution of Instruction • Stack operation • Peripheral operations • Reset, Interrupt, ready and hold

21. Flag register S : after the execution of an arithmetic operation, if bit 7 of the result is 1, then sign flag is set. Z : bit is set if ALU operation results a zero in the Acc or registers. AC: bit is set, when a carry is generated by bit 3 and passed on bit 4. P: parity bit is set when the result has even number of 1s. CY = carry is set when result generates a carry. Also a borrow flag. S Z AC P CY

22. Accumulator • Hold data for manipulation (arithmetic, logical). • Whenever the operation combines two words, either arithmetically or logically, the accumulator contains one word (say A) and the other word (say B) may be contained in a register or in memory location. After the operation the result is placed in the Acc replacing the word A. • Major working register. MP can directly work on Acc. • Programmed data transfer.

23. General purpose registers • Six registers. • B, C, D, E, H and L can store 8 bit data. • They can be combined to perform some 16 bit operation.

24. ALU • Arithmetic logic unit. • Two input ports, one output port. • Perform AND, OR, ExOR, Add, subtract, complement, Increment, Decrement, shift left, shift right. • ALUs one temporary registers are connected to MPs internal bus from which it can take data from any registers. It can place data directly to data bus through its single output port.

25. Program counter • Its job is to keep track of what instruction is being used and what the next instruction will be. • For 8085 it is 16 bit long. • Can get data from internal bus as well as memory location. • PC automatically increments to point to the next memory during the execution of the present instruction. • PC value can be changed by some instructions.

26. Stack pointer • 16 bit register acts as memory pointer. • Can save the value of the program counter for later use. • points to a region of memory which is called stack. follows LIFO algorithm. • After every stack operation SP points to next available location of the stack. Usually decrements.

27. Memory address register • PC sends address to MAR. MAR points to the location of the memory where the content is to be fetched from. • PC increments but MAR does not. • If the content is an instruction, IR decodes it. During execution if it is required to fetch another word from memory, PC is loaded with the value • PC again sends it to the MAR and fetch operation starts.

28. Instruction register • Holds instruction the microprocessor is currently being executed. • 8 bit long.

29. others • Instruction decoder. • Control logic. • Internal data bus.

30. Machine cycle and Timing dia • MP works in steps of clock. Each clock cycle is called T-state. • A machine cycle is composed a few T-states and performs either read or write operations. • All MP instructions are divided into few machine cycles. • Opcode fetch • Memory read • Memory write • IO read • IO write

31. Timing diaga. of Memory cycle T1 T2 T3 T1 T2 T3 CLK A15-A8 Data from memory A7-A0 Data from MPU AD7-AD0 A7-A0 ALE IO/M RD WR MEMRD MEMWR WRITE Cycle READ Cycle

32. MVI A,32H Instruction 2000H 3EH ;MVI A, 32H 2001H 32H M1 (Opcode-fetch) M2 (Memory Read) T3 T1 T2 T3 T2 T4 T1 A15-A8 20H; high-order address Unspecified 20H; High-order address 01H; low-order Add 00H; low-order Add 32H; Data AD7-AD0 3E; opcode ALE Status IO/M=0,S1=1,S0=1; opcode fetch Status IO/M=0,S1=1,S0=0; data read RD

33. Execution time • Clock frequency f = 2 MHz • T-state = (1/f) = 0.5 µs • Exec time for opcode fetch= (4Tx0.5)=2 µs. • Exec time for memory read = 3Tx0.5=1.5 µs. • Exec time for instruction = 7Tx0.5 = 3.5 µs.

34. 8085 5V GND 40 20 21 – 28 HIGH ORDER ADD BUS X1 X2 • 40 pin DIP. • +5V • 3 - 5MHz • ADD BUS • DATA BUS • CONTROL STATUS • POWER SUPPLY AND FREQ • EXTERNALLY INITIATED SIGNALS • SERIAL I/O PORTS SID 5 SOD 4 TRAP 6 12 – 19 MUX ADD/ DATA BUS RST7.5 7 RST6.5 8 RST5.5 9 INTR 10 30 ALE 29 S0 READY 35 HOLD 39 33 S1 RESET IN 36 34 IO/M’ 32 RD’ INTA 11 31 WR’ HLDA 38 3 37 CLK OUT RESET OUT

35. 8085 has the clock generation circuit on the chip. 8085 can operate maximum 3.03 MHz and 8085A-2 can operate maximum 5 MHz clock. • crystal, LC tuned, external clock ckt. • the frequency at x1x2 is divided by 2 internally. This means that in order to obtain 3.03MHz, a clock source of 6.06MHz must be connected to X1X2. • for crystals with less than 4MHz, a capacitor of 20pF should be connected X2 and ground. X1 X2 GND X1 X2

36. A15 Address bus. higher 8 bit A8 ALE G AD7 D Q’ AD6 Address bus. Lower 8 bit AD5 OC AD0 GND Data bus ADD/DATA bus • Address bus 16 bits • A8 to A15 unidirectional. Higher 8 bit • AD0 to AD7 multiplexed with data. This pins are bidirectional when used as data bus. • Data bus 8 bit long: AD0 to AD7

37. Machine cycle IO/M’ S1 S0 Control signals Opcode fetch 0 1 1 RD=0 Memory read 0 1 0 RD=0 Memory write 0 0 1 WR=0 I/O read 1 1 0 RD=0 I/O write 1 0 1 WR=0 Interrupt Ackn 1 1 1 INTA=0 Halt Z 0 0 RD, WR =Z and INTA=1 Hold Z X X Reset Z X X Control signals • ALE – active high output used to latch the lower 8 address bits. • RD, WR - active low output signals. • IO/M – output signal to differentiate memory and IO operation. • S1 and S0 – status output signal. Identify various operations.

38. External control signals • INTR – interrupt request. Input signal • INTA – interrupt acknowledge. o/p signal. • RST7.5,RST 6.5, RST5.5 – restart interrupts. Vectored interrupts. Higher priority. • TRAP - Nonmaskable interrupt. Highest priority. • Hold – request for the control of buses. I/P signal • HLDA – Hold Acknowledge. O/P signal • READY – I/P signal. When low, Mp waits for integral number of clock cycles until it goes high.

39. Interfacing I/O devices • Port address • Two ways to interface • IO mapped I/O • Memory mapped IO • 8085 • IO address space 256 (i.e 28) • Memory address space 64K (i.e 216)

40. Interfacing approach • Port address • An address where a buffer or latch is connected through which actual data transfer takes place between MP and IO device. • Input port or output port. • IO mapped IO • The port address of the IO devices is mapped into the IO address space • Port address is an eight bit binary number. IN/OUT instructions are used data transfer. • Memory Mapped IO • The port address of the IO device is mapped into the memory address space. • Port address is a 16 bit binary number. LDA, STA etc memory related instructions are used for data transfer.

41. Logic devices for interfacing • Tri-state buffer • At input port • 74LS244: unidirectional octal buffer • 74LS245: bidirectional octal buffer • Latches • At output port • 74LS373: Octal D type latch • Decoder • For address decoding, port selection, but control signal • 74LS138: 3-to-8 decoder most commonly used. • Encoder • For interfacing keyboard • 74LS148: 8 to 3 priority encoder

42. Peripheral I/O instructions • port address: 50H 2050 D3 2051 50 • Let input port address is 30H 2150 DB 2151 30 OUT 50H sends acc content to I/O address 50H IN 30H reads content from I/O address 30H and stores the value in accum

43. Device selection & Data Transfer • Decode the IO address. • Combine it with control the signal to generate a unique IO select pulse that is generated only when both signals are asserted. • Use it to activate the IO port • Address decoding can be absolute or partial IOR or IOW Address lines Decoder NOR Enable To Peripherals Data bus Latch Or Tri-state Buffer

44. 21H 51H Port addre 30H IN 30H instruction M1 M2 M3 T1 T2 T3 T4 T1 T2 T3 T1 T2 T3 CLK unspecified 21H Port add 30H A15-A8 Data from Accumula DB from memory 50H AD7-AD0 Port add 30H ALE IO/M RD MEMRD IORD

45. unspecified 20H 20H Port add, 50H Port addre 50H Opcode D3 Data from Accumula Port add 50H 50H 51H OUT 50H instruction M1 M2 M3 T1 T2 T3 T4 T1 T2 T3 T1 T2 T3 CLK A15-A8 AD7-AD0 ALE IO/M RD MEMRD WR IOWR

46. Interfacing LED for display • Given port add: FFH • Use octal latch as o/p port. • Steps for IO select pulse: • Decode FF • Use IO/M to make the port I/O mapped only • Use WR signal to write data to the port

47. MVI A, data OUT FFH HLT A7 IOADR A1 WR A0 * To interface a 7-segment display you need to decide about the type of 7-segment: common anode or common cathode * Power supply connection to the LED segments will be opposite. * For common cathode a 0 is sent to the respective pin to lit it up. IOSEL IO/M +5 V G D7 D FF D6 Octal D- latch D0 OE

48. Interfacing DIP switches • Let port address: 07H – 00H • Partial decoding • Must use pull-up resistors. IN 07H instruction reads a byte into accumulator from port 07H A3 IO/M A4 RD Q0 A7 E1 E2 E3 3 to 8 decoder A6 IOSEL A5 OE D7 D1 D0 +5 V

49. Interfacing 7 segment LED o/p address F9h A7 A6 A5 A4 A3 IO/M WR Q5 A2 E1 E2 E3 3 to 8 decoder A7 A6 A5 A4 A3 A2 A1 A0 A1 IOSEL 1 1 1 1 1 1 0 1 A0 +5V OE 74LS377 D7 D6 D0 D FF 7-Segment

50. 8085 Interrupts • 5 interrupt pins • Maskable • INTR • RST5.5, RST6.5, RST7.5 • Non-Maskable • TRAP: cannot be disabled by instruction. • TRAP has highest priority • Once a interrupt is serviced all interrupts except TRAP is disabled