The 8088 and 8086 Microprocessors  The 8086, announced in 1978, was the first 16- bit microprocessor introduced by Intel Corporation  8086 and 8088 are internally 16-bit MPU. Externally the 8086 has a 16-bit data bus and the 8088 has an 8-bit data bus

The 8088 and 8086 Microprocessors (cont.)  8086 and 8088 both have the ability to address up to 1 Mbyte of memory and 64K of input/output port  The 8088 and 8086 are both manufactured using high-performance metal-oxide semiconductor (HMOS) technology  The 8088 and 8086 are housed in a 40-pin dual inline package and many pins have multiple functions

The 8088 and 8086 Microprocessors (cont.)  CMOS, Complementary Metal-Oxide- Semiconductor, is a major class of integrated circuits used in chips such as microprocessors, microcontrollers, static RAM, digital logic circuits, and analog circuits such as image sensors  Two important characteristics of CMOS devices are high noise immunity and low static power supply drain.  Significant power is only drawn when its transistors are switching between on and off states

The 8088 and 8086 Microprocessors (cont.)  CMOS devices do not produce as much heat as other forms of logic such as TTL.  CMOS also allows a high density of logic functions on a chip

The 8088 and 8086 Microprocessors (cont.) Pin layout of the 8086 and 8088 microprocessor

16-bit Arithmetic Logic Unit 16-bit data bus (8088 has 8-bit data bus) 20-bit address bus = 1,048,576 = 1 meg The address refers to a byte in memory. In the 8088, these bytes come in on the 8-bit data bus. In the 8086, bytes at even addresses come in on the low half of the data bus (bits 0-7) and bytes at odd addresses come in on the upper half of the data bus (bits 8-15). The 8086 can read a 16-bit word at an even address in one operation and at an odd address in two operations. The 8088 needs two operations in either case. The least significant byte of a word on an 8086 family microprocessor is at the lower address Features

Simplified CPU Design

Intel 16-bit Registers

The 8086 has two parts, the Bus Interface Unit (BIU) and the Execution Unit (EU). The BIU fetches instructions, reads and writes data, and computes the 20-bit address. The EU decodes and executes the instructions using the 16-bit ALU. The BIU contains the following registers: IP - the Instruction Pointer CS - the Code Segment Register DS - the Data Segment Register SS - the Stack Segment Register ES - the Extra Segment Register The BIU fetches instructions using the CS and IP, written CS:IP, to contract the 20-bit address. Data is fetched using a segment register (usually the DS) and an effective address (EA) computed by the EU depending on the addressing mode Architecture

The EU contains the following 16-bit registers: AX - the Accumulator BX - the Base Register CX - the Count Register DX - the Data Register SP - the Stack Pointer \ defaults to stack segment BP - the Base Pointer / SI - the Source Index Register DI - the Destination Register These are referred to as general-purpose registers, although, as seen by their names, they often have a special-purpose use for some instructions. The AX, BX, CX, and DX registers can be considers as two 8-bit registers, a High byte and a Low byte. This allows byte operations and compatibility with the previous generation of 8-bit processors, the 8080 and source code could be translated in 8086 code and assembled. The 8-bit registers are: AX --> AH,AL BX --> BH,BL CX --> CH,CL DX --> DH,DL

8086 Programmer’s Model ES CS SS DS IP AH BH CH DH AL BL CL DL SP BP SI DI FLAGS AX BX CX DX Extra Segment Code Segment Stack Segment Data Segment Instruction Pointer Accumulator Base Register Count Register Data Register Stack Pointer Base Pointer Source Index Register Destination Index Register BIU registers (20 bit adder) EU registers

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 8086/8088 Microprocessors: Registers Registers –Registers are in the CPU and are referred to by specific names –Data registers Hold data for an operation to be performed There are 4 data registers (AX, BX, CX, DX) –Address registers Hold the address of an instruction or data element Segment registers (CS, DS, ES, SS) Pointer registers (SP, BP, IP) Index registers (SI, DI) –Status register Keeps the current status of the processor On an IBM PC the status register is called the FLAGS register –In total there are fourteen 16-bit registers in an 8086/8088

Data Registers: AX, BX, CX, DX Instructions execute faster if the data is in a register AX, BX, CX, DX are the data registers Low and High bytes of the data registers can be accessed separately –AH, BH, CH, DH are the high bytes –AL, BL, CL, and DL are the low bytes Data Registers are general purpose registers but they also perform special functions AX –Accumulator Register –Preferred register to use in arithmetic, logic and data transfer instructions because it generates the shortest Machine Language Code –Must be used in multiplication and division operations –Must also be used in I/O operations

BX –Base Register –Also serves as an address register –Used in array operations –Used in Table Lookup operations (XLAT) CX –Count register –Used as a loop counter –Used in shift and rotate operations DX –Data register –Used in multiplication and division –Also used in I/O operations

Pointer and Index Registers Contain the offset addresses of memory locations Can also be used in arithmetic and other operations SP: Stack pointer –Used with SS to access the stack segment BP: Base Pointer –Primarily used to access data on the stack –Can be used to access data in other segments SI: Source Index register –is required for some string operations –When string operations are performed, the SI register points to memory locations in the data segment which is addressed by the DS register. Thus, SI is associated with the DS in string operations.

DI: Destination Index register –is also required for some string operations. –When string operations are performed, the DI register points to memory locations in the data segment which is addressed by the ES register. Thus, DI is associated with the ES in string operations. The SI and the DI registers may also be used to access data stored in arrays

Segment Registers - CS, DS, SS and ES Are Address registers Store the memory addresses of instructions and data Memory Organization –Each byte in memory has a 20 bit address starting with 0 to or 1 meg of addressable memory –Addresses are expressed as 5 hex digits from FFFFF –Problem: But 20 bit addresses are TOO BIG to fit in 16 bit registers! –Solution: Memory Segment Block of 64K (65,536) consecutive memory bytes A segment number is a 16 bit number Segment numbers range from 0000 to FFFF Within a segment, a particular memory location is specified with an offset An offset also ranges from 0000 to FFFF

Segmented Memory Segmented memory addressing: absolute (linear) address is a combination of a 16-bit segment value added to a 16- bit offset linear addresses one segment

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

Example Address Calculation If the data segment starts at location 1000h and a data reference contains the address 29h where is the actual data? Intel Offset: Segment: Address:

Segment:Offset Address Logical Address is specified as segment:offset Physical address is obtained by shifting the segment address 4 bits to the left and adding the offset address Thus the physical address of the logical address A4FB:4872 is A4FB A9822

Your turn... What linear address corresponds to the segment/offset address 028F:0030? 028F = Always use hexadecimal notation for addresses.

Your turn... What segment addresses correspond to the linear address 28F30h? Many different segment-offset addresses can produce the linear address 28F30h. For example: 28F0:0030, 28F3:0000, 28B0:0430,...

The Code Segment Memory Segment Register Offset Physical or Absolute Address 0 + CS: IP 0400H 0056H 4000H 4056H H The offset is the distance in bytes from the start of the segment. The offset is given by the IP for the Code Segment. Instructions are always fetched with using the CS register. CS:IP = 400:56 Logical Address 0H 0FFFFFH The physical address is also called the absolute address.

The Data Segment Memory Segment Register Offset Physical Address + DS: EA 05C C00H 05C50H 05C C50H Data is usually fetched with respect to the DS register. The effective address (EA) is the offset. The EA depends on the addressing mode. DS:EA 0H 0FFFFFH

The Stack Segment Memory Segment Register Offset Physical Address + SS: SP 0A A000H 0A100H 0A A100H The stack is always referenced with respect to the stack segment register. The stack grows toward decreasing memory locations. The SP points to the last or top item on the stack. PUSH - pre-decrement the SP POP - post-increment the SP The offset is given by the SP register. SS:SP 0H 0FFFFFH

Flags Carry flag Parity flag Auxiliary flag Zero Overflow Direction Interrupt enable Trap Sign 6 are status flags 3 are control flag

CF (carry) Contains carry from leftmost bit following arithmetic, also contains last bit from a shift or rotate operation. Flag Register FlagODITSZAPC Bit no Conditional flags: –They are set according to some results of arithmetic operation. You do not need to alter the value yourself. Control flags: –Used to control some operations of the MPU. These flags are to be set by you in order to achieve some specific purposes.

Flag Register OF (overflow) Indicates overflow of the leftmost bit during arithmetic. DF (direction) Indicates left or right for moving or comparing string data. IF (interrupt) Indicates whether external interrupts are being processed or ignored. TF (trap) Permits operation of the processor in single step mode.

SF (sign) Contains the resulting sign of an arithmetic operation (1=negative) ZF (zero) Indicates when the result of arithmetic or a comparison is zero. (1=yes) AF (auxiliary carry) Contains carry out of bit 3 into bit 4 for specialized arithmetic. PF (parity) Indicates the number of 1 bits that result from an operation.

Minimum-Mode and Maximum- Mode System 

Minimum-Mode and Maximum- Mode System (cont.) Signals common to both minimum and maximum mode

Minimum-Mode and Maximum- Mode System (cont.) Unique minimum-mode signals

Minimum-Mode and Maximum- Mode System (cont.) Unique maximum-mode signals

 Minimum-Mode and Maximum- Mode System (cont.)

Minimum-Mode Interface Block diagram of the minimum-mode 8088 MPU

Minimum-Mode Interface (cont.) Block diagram of the minimum-mode 8086 MPU

Minimum-Mode Interface (cont.)  The minimum-mode signals can be divided into the following basic groups: Address/Data bus Status signals Control signals Interrupt signals DMA interface signals

Minimum-Mode Interface (cont.)  Address/Data bus The address bus is used to carry address information to the memory and I/O ports The address bus is 20-bit long and consists of signal lines A 0 through A 19  A 20-bit address gives the 8088 a 1 Mbyte memory address space Only address line A 0 through A 15 are used when addressing I/O.  This give an I/O address space of 64 Kbytes The 8088 has 8 multiplexed address/data bus lines (A 0 ~A 7 ) 8086 has 16 multiplexed address/data bus lines (A 0 ~A 15 )

Minimum-Mode Interface (cont.)  Status signals The four most significant address, A 19 through A 16 are multiplexed with status signal S 6 through S 3  Bits S 4 and S 3 together form a 2-bit binary code that identifies which of the internal segment registers was used to generate the physical address.  S 5 is the logic level of the internal interrupt flag.  S 6 is always at the 0 logic level

Minimum-Mode Interface (cont.) 

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Maximum-Mode Interface  The maximum-mode configuration is mainly used for implementing a multiprocessor/coprocessor system environment Multiple processors exist in the system Each executes its own program  Global resources and local resources The former are common to all processors The latter are assigned to specific processors  In the maximum-mode, facilities are provided for implementing allocation of global resources and passing bus control to other microprocessors sharing the system bus

Maximum-Mode Interface (cont.) 8088 maximum-mode block diagram

Maximum-Mode Interface (cont.) 8086 maximum-mode block diagram

Maximum-Mode Interface (cont.)  8288 bus controller Block diagram and pin layout of 8288

Maximum-Mode Interface (cont.)  8288 bus controller In the maximum-mode, 8088/8086 outputs a status code on three signal line, S 0, S 1, S 2, prior to the initialization of each bus cycle The 3-bit bus status code identifies which type of bus cycle is to follow and are input to the external bus controller device, 8288 The 8288 produces one or two command signals for each bus cycle

Maximum-Mode Interface (cont.)  8288 bus controller Bus status code

Maximum-Mode Interface (cont.) 

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 Queue status signals The 2-bit queue status code QS0 and QS1 tells the external circuitry what type of information was removed form the queue during the previous clock cycle Queue status code

Electrical Characteristics  Power is applied between pin 40 (V cc ) and pins 1 (GND) and 20 (GND)  The nominal value of V cc is specified as +5V dc with a tolerance of ±10%.  Both 8088 and 8086 draw a maximum of 340mA from the supply I/O voltage levels

System Clock  The time base for synchronization of the internal and external operations of the microprocessor in a microcomputer system is provided by the clock (CLK) input signal The standard 8088 operates at 5 MHz and the operates at 8 MHz  The 8086 is manufactured in three speeds: 5- MHz 8086, 8-MHz , and the 10-MHz  The CLK is externally generated by the 8284 clock generator and driver IC

System Clock (cont.)  Block diagram of the 8284 clock generator

System Clock (cont.)  Block diagram of the 8284 clock generator

System Clock (cont.)  Connecting the 8284 to the or 24MHz crystal Typical value of CL when used with 15MHz crystal is 12pF The fundamental crystal frequency is divided by 3 within the 8284 to give either a 5- or 8- MHz clock signal

System Clock (cont.)  CLK waveform The signal is specified at Metal Oxide Semiconductor (MOS)-compatible voltage level The period of the 5-MHz 8088 can range from 200 ns to 500 ns, and the maximum rise and fall times of its edges equal 10 ns

System Clock (cont.)  PCLK and OSC signals The peripheral clock (PCLK) and oscillator clock (OSC) signals are provided to drive peripheral ICs The clock output at PCLK is half the frequency of CLK. The OSC output is at the crystal frequency which is three times of CLK

System Clock (cont.)  The 8284 can also be driven from an external clock source Applied to the EFI (External Frequency Input) Input F/C is used for selection  0: crystal between X 1 and X 2 is used  1: selects EFI  The CSYNC input is used for external synchronization in systems with multiple clocks

System Clock (cont.)  EXAMPLE If the CLK input of an 8086 MPU is to be driven by a 9-MHz signal, what speed version of the 8086 must be used and what frequency crystal must be attached to the 8284  Solution: The is the version of the 8086 that can be run at 9-MHz. To create the 9-MHz clock, a 27-MHz crystal must be used on the 8284.

Bus Cycle and Time States  A bus cycle defines the basic operation that a microprocessor performs to communicate with external devices.  Examples of bus cycles are the memory read, memory write, input/output read, and input/output write.  The bus cycle of the 8088 and 8086 microprocessors consists of at least four clock periods.  If no bus cycles are required, the microprocessor performs what are known as idle states.  When READY is held at the 0 level, wait states are inserted between states T3 and T4 of the bus cycle.

Bus Cycle and Time States (cont.) Bus cycle clock periods, idle state, and wait state

Bus Cycle and Time States (cont.)  EXAMPLE What is the duration of the bus cycle in the based microcomputer if the clock is 8 MHz and the two wait states are inserted.  Solution: The duration of the bus cycle in an 8 MHz system is given by  t cyc = 500 ns + N x 125 ns In this expression the N stands for the number of waits states. For a bus cycle with two wait states, we get  t cyc = 500 ns + 2 x 125 ns = 500 ns ns = 750 ns

Hardware Organization of the Memory Address Space 1Mx8 memory bank of the 8088

Hardware Organization of the Memory Address Space (cont.) High and low memory banks of the 8086

Hardware Organization of the Memory Address Space (cont.) Byte transfer by the 8088

Hardware Organization of the Memory Address Space (cont.) Word transfer by the 8088

Hardware Organization of the Memory Address Space (cont.) Even address byte transfer by the 8086

Hardware Organization of the Memory Address Space (cont.) Odd address byte transfer by the 8086

Hardware Organization of the Memory Address Space (cont.) Even address word transfer by the 8086

Hardware Organization of the Memory Address Space (cont.) Odd-address word transfer by the 8086

Hardware Organization of the Memory Address Space (cont.)  EXAMPLE Is the word at memory address of an 8086-based microcomputer aligned or misaligned? How many cycle are required to read it from memory?  Solution: The first byte of the word is the second byte at the aligned-word address Therefore, the word is misaligned and required two bus cycles to be read from memory.

Address Bus Status Codes  Whenever a memory bus cycle is in progress, an address bus status code S 4 S 3 is output by the processor. S 4 S 3 identifies which one of the four segment register is used to generate the physical address in the current bus cycle:  S 4 S 3 =00 identifies the extra segment register (ES)  S 4 S 3 =01 identifies the stack segment register (SS)  S 4 S 3 =10 identifies the code segment register (CS)  S 4 S 3 =11 identifies the data segment register (DS)  The memory address reach of the microprocessor can thus be expanded to 4 Mbytes.

Memory Control Signals  Minimum-mode memory control signals

Memory Control Signals (cont.)  Minimum-mode memory control signals (8088) ALE – Address Latch Enable – used to latch the address in external memory. IO/M – Input-Output/Memory – signal external circuitry whether a memory of I/O bus cycle is in progress. DT/R – Data Transmit/Receive – signal external circuitry whether the 8088 is transmitting or receiving data over the bus. RD – Read – identifies that a read bus cycle is in progress. WR – Write – identifies that a write bus cycle is in progress. DEN – Data Enable – used to enable the data bus. SSO – Status Line – identifies whether a code or data access is in progress.

Memory Control Signals (cont.)  The control signals for the 8086 ’ s minimum- mode memory interface differs in three ways: IO/M signal is replaced by M/IO signal. The signal SSO is removed from the interface. BHE (bank high enable) is added to the interface and is used to select input for the high bank of memory in the 8086 ’ s memory subsystem.

Memory Control Signals (cont.)  Maximum-mode memory control signals

Memory Control Signals (cont.)  Maximum-mode memory control signals MRDC – Memory Read Command MWTC – Memory Write Command AMWC – Advanced Memory Write Command

Read and Write Bus Cycle  Read cycle Minimum-mode memory read bus cycle of the 8088

Read and Write Bus Cycle (cont.)  Read cycle Minimum-mode memory read bus cycle of the 8086

Read and Write Bus Cycle (cont.)  Read cycle Maximum-mode memory read bus cycle of the 8086

Read and Write Bus Cycle (cont.)  Write cycle Minimum-mode memory write bus cycle of the 8088

Read and Write Bus Cycle (cont.)  Write cycle Maximum-mode memory write bus cycle of the 8086

Memory Interface Circuit  Address bus latches and buffers  Bank write and bank read control logic  Data bus transceivers/buffers  Address decoders

Memory Interface Circuit (cont.) Memory interface block diagram

Memory Interface Circuit (cont.)  Address bus latches and buffers Block diagram of a D-type latch

Memory Interface Circuit (cont.)  Address bus latches and buffers Circuit diagram of the 74F373

Memory Interface Circuit (cont.)  A review of flip-flop/latch logic Positive edge-triggered D flip-flop

Memory Interface Circuit (cont.)  A review of flip-flop/latch logic Positive edge-triggered JK flip-flop

Memory Interface Circuit (cont.)  A review of flip-flop/latch logic D-type latch

Memory Interface Circuit (cont.)  Address bus latches and buffers Address latch circuit

Memory Interface Circuit (cont.)  Bank write and bank read control logic Bank write control logicBank read control logic

Memory Interface Circuit (cont.)  Data bus transceivers Block diagram and circuit diagram of the 74F245 octal bus transceiver

Memory Interface Circuit (cont.)  Data bus transceivers Data bus transceiver circuit

Memory Interface Circuit (cont.)  Address decoder Address bus configuration with address decoding

Memory Interface Circuit (cont.)  Address decoder Block diagram and operation of the 74F139 decoder

Memory Interface Circuit (cont.)  Address decoder Circuit diagram of the 74F139 decoder

Memory Interface Circuit (cont.)  Address decoder Address decoder circuit using 74F139

Memory Interface Circuit (cont.)  Address decoder Block diagram and operation of the 74F138 decoder

Memory Interface Circuit (cont.)  Address decoder Circuit diagram of the 74F138 decoder

Memory Interface Circuit (cont.)  Address decoder Address decoder circuit using 74F138

Types of Input/Output  The I/O system allows peripherals to provide data or receive results of processing the data Using I/O ports  The 8088/8086 MPU can employ two types of I/O Isolated I/O Memory-mapped I/O  They differ in how I/O ports are mapped into the address space

Types of Input/Output (cont.)  Isolated input/output When using isolated I/O in a microcomputer system, the I/O device are treated separate from memory  The memory address space contains 1 M consecutive byte address in the range through FFFFF 16  The I/O address space contains 64K consecutive byte addresses in the range through FFFF 16 The bytes in two consecutive I/O addresses can be accessed as word-wide data Page 0:  00FF 16  Certain I/O instructions can only perform in this range

Types of Input/Output (cont.)  Isolated input/output 8088/8086 memory and I/O address spaces

Types of Input/Output (cont.)  Isolated input/output Isolated I/O ports

Types of Input/Output (cont.)  Isolated input/output Advantages:  The complete 1Mbyte memory address space is available for use with memory  Special instructions have been provided to perform I/O operations with maximized performance The bytes in two consecutive I/O addresses can be accessed as word-wide data Disadvantages:  All input and output data transfers must take place between the AL or AX register and I/O port

Types of Input/Output (cont.)  Memory-mapped input/output MPU looks at the I/O port as though it is a storage location in memory  Some of the memory address space is dedicated to I/O ports Instructions that affect data in memory are used instead of the special I/O instructions  More instructions and addressing modes are available to perform I/O operations  I/O transfers can take place between I/O port and other internal registers The memory instructions tend to execute slower than those specifically designed for isolated I/O Part of the memory address space is lost

Types of Input/Output(cont.)  Memory-mapped input/output Memory mapped I/O ports

Isolated Input/Output Interface  I/O devices: Keyboard Printer Mouse 82C55A, etc  Functions of interface circuit: Select the I/O port Latch output data Sample input data Synchronize data transfer Translate between TTL voltage levels and those required to operate the I/O devices

Isolated Input/Output Interface (cont.)  Minimum-mode interface Minimum-mode 8088 system I/O interface

Isolated Input/Output Interface (cont.)  Minimum-mode interface Minimum-mode 8086 system I/O interface

Isolated Input/Output Interface (cont.)  Maximum-mode interface Maximum-mode 8088 system I/O interface

Isolated Input/Output Interface (cont.)  Maximum-mode interface Maximum-mode 8086 system I/O interface

Isolated Input/Output Interface (cont.)  Maximum-mode interface I/O bus cycle status codes

Input/Output Data Transfer  Input/output data transfers in the 8088 and 8086 microcomputers can be either byte-wide or word-wide  I/O addresses are 16 bits in length and are output by the 8088 to the I/O interface over bus lines AD0 through AD7 and A8 through A15  In 8088, the word transfers is performed as two consecutive byte-wide data transfer and takes two bus cycle  In 8086, the word transfers can takes either one or two bus cycle  Word-wide I/O ports should be aligned at even-address boundaries

Input/Output Data Instructions

Input/Output Data Instructions (cont.) EXAMPLE: Write a sequence of instructions that will output the data FF 16 to a byte-wide output port at address AB 16 of the I/O address space. Solution: First, the AL register is loaded with FF16 as an immediate operand in the instruction MOV AL, 0FFH Now the data in AL can be output to the byte- wide output port with the instruction OUT 0ABH, AL

Input/Output Data Instructions (cont.) EXAMPLE: Write a series of instructions that will output FF 16 to an output port located at address B of the I/O address space Solution: The DX register must first be loaded with the address of the output port. This is done with the instruction MOV DX, 0B000H Next, the data that are to be output must be loaded into AL with the instruction MOV AL, 0FFH Finally, the data are output with the instruction OUT DX, AL

Input/Output Data Instructions (cont.) EXAMPLE: Data are to be read in from two byte-wide input ports at addresses AA 16 and A9 16 and then output as a word-wide output port at address B Write a sequence of instructions to perform this input/output operation.

Input/Output Data Instructions (cont.) Solution: First read in the byte at address AA 16 into AL and move it into AH. IN AL, 0AAH MOV AH, AL Now the other byte can be read into AL by the instruction IN AL, 09AH And to write out the word of data MOV DX, 0B000H OUT DX, AX

Input/Output Bus Cycles  Input bus cycle of the 8088

Input/Output Bus Cycles (cont.)  Output bus cycle of the 8088

Input/Output Bus Cycles (cont.)  Input bus cycle of the 8086

Input/Output Bus Cycles (cont.)  Output bus cycle of the 8086