Microprocessor History

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.

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.

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.

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.

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

Modern MP Pentium Pentium Pro Pentium MMX Pentium II, III, IV RISC 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.

MP based system MP memory IO device

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 Instruction Register Register Array ALU Control Bus control Address Bus

Memory Interfacing and IO decoding

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

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.

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.

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

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

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

Interfacing A Memory Chip 2K Byte memory Memory address space of the chip: 8800H to 8FFFH A14 IO/M A15 A13 3 to 8 decoder E1 E2 E3 A12 MEMSEL Q1 A11 A10 Memory Chip CE 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 8 8 - F 0 - F 0 - F RD WR

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.

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

MP operations MP initiated Operations Internal 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

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

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.

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.

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.

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.

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.

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.

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

others Instruction decoder. Control logic. Internal data bus.

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

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

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

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.

8085 40 pin DIP. +5V 3 - 5MHz ADD BUS DATA BUS CONTROL STATUS 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 HLDA 38 3 37 31 WR’ RESET OUT CLK OUT

crystal, LC tuned, external clock ckt. 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

ADD/DATA bus Address bus 16 bits Data bus 8 bit long: AD0 to AD7 Q’ OC AD7 AD6 AD5 AD0 ALE GND Address bus. Lower 8 bit Address bus. higher 8 bit A8 A15 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

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. Machine cycle IO/M’ S1 S0 Control signals Opcode fetch 1 RD=0 Memory read Memory write WR=0 I/O read I/O write Interrupt Ackn INTA=0 Halt Z RD, WR =Z and INTA=1 Hold X Reset

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.

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)

Interfacing approach Port address IO mapped IO Memory Mapped IO 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.

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

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

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 Address lines IOR or IOW Decoder NOR Enable To Peripherals Data bus Latch Or Tri-state Buffer

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

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

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

* Power supply connection to the LED segments will be opposite. 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. IO/M IOSEL +5 V G D7 D FF D6 Octal D- latch D0 OE

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 A4 A3 IO/M Q0 RD A7 3 to 8 decoder E1 E2 E3 A6 IOSEL A5 OE D7 D1 D0 +5 V

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

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

TRAP cannot be disabled by instruction Requires a High level with a leading eadge at the pin. braches to location 0024H. disabled at the falling edge of the signal at the pin.

RST7.5,6.5,5.5 can be enabled or disabled by SIM (Set Interrupt Mask). 7.5 – Leading edge. branches to 003CH. 6.5,5.5 – High level. 6.5: branches to 0034H 5.5: branches to 0020H

INTR Interrupt process enable by writing EI. mp checks INTR line at each instruction. if INTR is high, mp completes the current instr, disables Interrupt Flip-flop, sends INTA signal. An RST instru is inserted by INTA through external hardware. Mp saves the memory address of the next instru into stack. Program control is transferred to CALL location. The service routine starts at CALL location. At the end of the subroutine Int Flag is enabled again by EI instru. The last instr of the subroutine is RET to trasfer back the prog control to its orginal address.

RST instructions 8 RST instructions +5v EF to data bus 1 1 1 1 1 1 1 Mnemonics Binary code Hex Call Location D7 D6 D5 D4 D3 D2 D1 D0 RST0 1 C7 0000 RST1 CF 0008 RST2 0010 RST3 DF 0018 RST4 E7 0020 RST5 EF 0028 RST6 F7 0030 RST7 FF 0038 +5v 1 1 EF to data bus 1 1 1 1 1 Enable

Write a program to count continuously in binary with some delay between each Count. Service routine at 8070H to flush FFH five times when the interrupt occurs (on INTR lines) with some appropriate delay between flash Main program Service routine 8070: SERV: PUSH B PUSH PSW MVI B, 0AH MVI A, 00H FLASH: OUT PORT1 CALL DELAY CMA DCR B JNZ FLASH POP PSW POP B EI RET LXI SP, FFFFH (stack region) EI MVI A, 00H NXTCNT: OUT PORT1 CALL DELAY (not defined here) INR A JMP NXTCNT RST 5 code EF +5V Interrupt instr: EF to data bus D7 1 1 1 1 At 0028H JMP 8070H 0028 C3 0029 70 002A 80 1 1 1 D0 INTA from µP

Description main program initializes stack pointer at FFFF and enables the interrupts. program will count continuously from 00 to FF with some delay between each count. To interrupt the process, a switch at INTR us pushed. the processor will complete the current instruction and senses the interrupt. Say the next instruction is INR A. µP disables the interrupt flip-flop, and sends out INTA signal. INTA enables the tri-state buffer and, and RST 5 (ie EF) is placed on the data bus. µP saves the address of the INR A instruction on the stack at locations FFFE and FFFD, and the program is transferred to memory location 0028. The location 0028 has the JMP 8070 instruction to transfer the program to the service routine.

Description contd. The program jumps to the service routine at 8070. The service routing saves the registers that are being used in the subroutine and loads the count ten in register B to output five flashes and five blanks. the service routine enables the interrupt before returning to main program. When the service routine executes the RET instruction, the µP retrieves the address of the instruction INR A from the stack and continues the binary counting.

Short Questions Ins there a minimum pulse width required for the INTR signal? 17.5 T states. CALL requir 18T states. µP check INTR signal one clock period before the last T states. How long can the INTR pulse stay high? until the interrupt flip-flop is set by EI instruction in the subroutine. Can the µP be interrupted again before the completion of the first interrupt service routine?

Vectored interrupts TRAP, RST 7.5,6.5 and 5.5 do not require external instruction to jump to its call locations. these interrupts are called vectored interrupts. maskable interrupts are enabled by two instructions: EI and SIM.

SIM Set Interrupt Mask. 7 SOD 6 SDE 5 XX 4 R7.5 3 MSE 2 M7.5 1 M6.5 M5.5 0=available, 1=masked no use 0 = ignore mask bits 1 = mask bits are enabled serial out data: ignored if bit 6 is 0 if 1, Reset 7.5 Enabling all interrupts: EI ; enable interrupts MVI A, 08h ; load bit patters for intr SIM ; Enables 7.5,6.5,5.5 if 1, bit 7 is serial data out

RIM Read Interrupt Mask. read to sense the pending interrupts. RIM loads accumulator with 8 bits indicating status of the interrupt masks. RIM can also be used to read serial data. 7 SID 6 I7.5 5 I6.5 4 I5.5 3 IE 2 M7.5 1 M6.5 M5.5 1 = pending 1 = masked 1 = Interrupt enabled Serial input data, if any

RIM example Assuming the µP is completing an RST7.5 interrupt request, check to see if RST6.5 is pending. If it is pending, enable RST6.5 without affecting any other interrupts; otherwise return to main program. RIM ; Read interrupt mask MOV B, A ; save mask info ANI 20h ;check if RST6.5 is pending JNZ NEXT ; EI RET ; RST6.5 is not pending; return to main program NEXT: MOV A,B ;get bit pattern; RST6.5 pending ANI 0Dh ; enables RST6.5 by setting D1=0 ORI 08h ;enable SIM by setting D3=1 SIM JMP SERV ; Jump service routing for RST6.5 at SERV

DMA Direct Memory Access HOLD HLDA IO device can transfer data from (to) memory directly. When µP controlled data transfer is too slow HOLD an input high signal to this pin initiated DMA. µP releases bus in the following machine cycle. gets back the control when HOLD is low. HLDA HOLD Ackn. After releasing the bus µP sends a high signal at this pin to inform the IO device.

DMA contd. Usually a DMA controller sends the DMA request to MP. The processor completes the current machine cycle; floats all the bus lines, and sends a ackn signal to HLDA. DMA controller takes the control of the buses and transfer data directly to memory from the external source by-passing µP. After data transfer DMA controller sends a low signal at HOLD pin to terminate the request for DMA. MP gets back its control over the buses. Address MPU DMA controller Memory IO control Data Bus HOLD HLDA

8086/8088 Architecture Seven categories of signals. Max/min mode: min mode is used for single procss. Max mode is used for multiprocss Test: synchronize multiple processors Data Enable: generally connected to biriectional buffer to isolate MPU from system bus. Data tran/rcvr: controls data flow. IO or memory: indicates whether the proc cycle is memory operation or IO operation. Bus High Enable: enble the higher order byte of 16 bit data Power & clock VCC CLK BHE/S7 A19/S6 A16/S3 AD15 AD0 ALE M/IO RD WR DEN DT/R MuX add & status signals GND INTR NMI HOLD READY RESET External rqst Mux add and data buses Response to External rqst INTA HOLDA Control & status signals Multipro envrnmnt TEST MN/MX

Max/min mode control signals Pin Min mode Max mode 24 INTA QS1: queue status signal 25 ALE QS0: queue stat signal 26 DEN S0: input sig to bus control 27 DT/R S1: “ 28 M/IO S2: “ 29 WR Lock: to prvnt another proc from gaining control 30 HLDA RQ/GT1: enable another processor to gain control 31 HOLD RQ/GT0: “

8086 Programming model 67

segment registers work together with general purpose register to access any memory value. For example if we would like to access memory at the physical address 12345h (hexadecimal), we should set the DS = 1230h and SI = 0045h. This is good, since this way we can access much more memory than with a single register that is limited to 16 bit values. CPU makes a calculation of physical address by multiplying the segment register by 10h and adding general purpose register to it (1230h * 10h + 45h = 12345h): by default BX, SI and DI registers work with DS segment register; BP and SP work with SS segment register. Other general purpose registers cannot form an effective address! also, although BX can form an effective address, BH and BL cannot.

special purpose registers IP - the instruction pointer. flags register - determines the current state of the microprocessor. IP register always works together with CS segment register and it points to currently executing instruction.

Memory Access [BX + SI] [BX + DI] [BP + SI] [BP + DI] [SI] [DI] d16 (variable offset only) [BX] [BX + SI + d8] [BX + DI + d8] [BP + SI + d8] [BP + DI + d8] [SI + d8] [DI + d8] [BP + d8] [BX + d8] [BX + SI + d16] [BX + DI + d16] [BP + SI + d16] [BP + DI + d16] [SI + d16] [DI + d16] [BP + d16] [BX + d16]

for example, let's assume that DS = 100, BX = 30, SI = 70 for example, let's assume that DS = 100, BX = 30, SI = 70. The following addressing mode: [BX + SI] + 25 is calculated by processor to this physical address: 100 * 16 + 30 + 70 + 25 = 1725. by default DS segment register is used for all modes except those with BP register, for these SS segment register is used. there is an easy way to remember all those possible combinations using this chart: you can form all valid combinations by taking only one item from each column or skipping the column by not taking anything from it. as you see BX and BP never go together. SI and DI also don't go together. here are an examples of a valid addressing modes:     [BX+5]     ,     [BX+SI]     ,     [DI+BX-4]

80286 16 bit Eliminates the multiplexing of buses. Has 24 bit linear address bus support 16M bytes address directly. Supports memory management through which it can support 1Gbytes of virtual memory. Protects system software from user programs, protects users’ program, and restricts access to some memory regions. Supports multiuser systems.

80386/486 32 bit processor. Support following multiuser system requirement High speed of execution Ability to handle different types of tasks efficiently Large memory space that can be shared by multiuser Appropriate memory allocations and the management of memory access Data security and data access Limited and selected access to part of the system Resource sharing and management

32bit non-multiplexed address bus Can address 4G physical memory and through a memory management unit 64 (246) terabytes of virtual memory. Two modes:real mode, and protected mode. Execution is highly pipelined.

80386 Programming model 8-general purpose registers can be accessed as 8, 16 or 32 bit 6-segment selector registers. IP can used as 16/32 bits Flag is 31 bits but 14 are used at present. 6 for data, 3 operation,2 io previl, 1 nested task, 2 for VM 31 15 7 AX BX CX DX SP BP SI DI CS SS DS ES FS GS IP FLAGS

Temperature control

Internal architecture of 8085 ALU