DX register This register is used to hold I/O port address for I/O instruction. A microcontroller is a small and low-cost microcomputer, which is designed to perform the specific tasks of embedded systems like displaying microwaves information, receiving remote signals, etc. Fetch stage can prefetch up to 6 bytes of instructions and stores them in the queue. When a microprocessor is executing a main program and whenever an interrupt occurs, the microprocessor shifts the control from the main program to process the incoming request. Learn more. Following is the table showing the list of Arithmetic instructions with their meanings. It has 9 flags and they are divided into 2 groups Conditional Flags and Control Flags. It supports data of type integer, float, and real types ranging from 2-10 bytes. It is also a 16-bit register works like stack, which is always incremented/decremented by 2 during push & pop operations. Now let us discuss the addressing modes in 8085 Microprocessor. General-purpose registers are used to store temporary data within the microprocessor. General Purpose Registers: These are numbered as R0, R1, R2.Rn-1, and used to store temporary data during any ongoing operation. Following table shows the result for various control inputs. This transfer of data can be either from register to register, register to memory or memory to register. If READY is low, then the CPU has to wait for READY to go high. BUSY It is an output signal, when it is high it indicates a busy state to the CPU. It is an edge triggered input, which causes an interrupt request to the microprocessor. It also contains 1 pointer register IP, which holds the address of the next instruction to executed by the EU. It is used to store the starting base address of the memory area within the data segment. The temporary storage locations inside the computer CPU to store data and addresses is called a register. It supports two modes of operation, i.e. the coprocessor is busy or idle. It is used to demultiplex the address-data signal of port. If any pin of this port is configured as an input, then it acts as if it floats, i.e. For odd number of 1s, the Parity Flag is reset. The interfacing process includes some key factors to match with the memory requirements and microprocessor signals. Pins 21 to 28 These pins are known as Port 2. Microprocessor performs three basic things while executing the instruction: A typical Microprocessor structure looks like this. When the signal is low, the microprocessor reads the data from the selected I/O port of the 8255. The CPU leaves the control over bus and acknowledges the HOLD request through HLDA signal. JG/JNLE Used to jump if greater/not less than/equal instruction satisfies. 8086 was the first 16-bit microprocessor available in 40-pin DIP (Dual Inline Package) chip. This port can be used for higher address byte with addresses A8-A15. It has four channels which can be used over four I/O devices. TYPE 1 interrupt represents single-step execution during the debugging of a program. These key-codes are de-bounced and stored in an 8-byte FIFORAM, which can be accessed by the CPU. In this chapter, we will discuss these operational modes. These instructions are used to perform operations where data bits are involved, i.e. So, the instruction The processing speed is so high that it can calculate multiplication of two 64-bits real numbers in ~27 s and can also calculate square-root in ~35 s. when it is high indicates IO operation and when it is low then it indicates memory operation. Microcontrollers are widely used in various different devices such as . These instructions are inserted into the program so that when the processor reaches there, then it stops the normal execution of program and follows the break-point procedure. In this mode, the data is transferred from one register to another by using the address pointed by the register. Pushes the Flag register values on to the stack. In the Slave mode, it enables the read/write operations to/from 8257. It is an acknowledgement signal from I/O devices that data is transferred. TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. POP Used to get a word from the top of the stack to the provided location. It was the first 16-bit processor having 16-bit ALU, 16-bit registers, internal data bus, and 16-bit external data bus resulting in faster processing. This signal is used to differentiate between IO and Memory operations, i.e. Till it is pulled low with a key closure, it is pulled up internally to keep it high. In order to apply logic 1 (5V) on this output pin, it is necessary to build an external pullup resistor. VCC indicates +5v power supply and VSS indicates ground signal. WR This signal indicates that the data on the data bus is to be written into a selected memory or IO location. It generates MARK signal to the peripheral device that 128 bytes have been transferred. When the pin is configured as an output, then it acts as an open drain. Hence, it is named as external memory microcontroller. NPG Used to negate each bit of the provided byte/word and add 1/2s complement. It is classified into five categories. Lower order address and data bus signals are multiplexed using this port. It also contains 1 pointer register IP, which holds the address of the next instruction to executed by the EU. The registers are the most easily accessible memory location for the CPU and sit on the top of the memory hierarchy. Data is sent or received one byte at a time. Its function is to control operations on data using the instruction decoder & ALU. it is active only when the overflow flag is set to 1 and branches to the interrupt handler whose interrupt type number is 4. It is expressed in megahertz (MHz) or gigahertz (GHz).It is also known as Clock Rate. X1, X2 A crystal (RC, LC N/W) is connected at these two pins and is used to set frequency of the internal clock generator. JAE/JNB Used to jump if above/not below instruction satisfies. When this interrupt is executed, the processor saves the content of the PC register into the stack and branches to 002CH address. Bydefault, it is enabled until it gets acknowledged. A Microprocessor is an important part of a computer architecture without which you will not be able to perform anything on your computer. AD0-AD7 carries low order byte data and AD8AD15 carries higher order byte data. Mode 2 In this mode, Port A can be configured as the bidirectional port and Port B either in Mode 0 or Mode 1. In the peripheral I/O mode, the RD and WR signals are connected to IOR and IOW, respectively. The coprocessor handles specialized tasks like mathematical calculations, graphical display on screen, etc. CISC stands for Complex Instruction Set Computer. RCR Used to rotate bits of byte/word towards the right, i.e. At present we have only used 48 bits of 64 bits so why require 128-bit address space. These are the processors which are designed for some special purposes. It is available at pin 32 and is used to read signal for Read operation. ALU performs arithmetical and logical operations on the data received from the memory or an input device. These lines can be programmed as encoded or decoded, using the mode control register. 8.1.2 Refresh Port Connections. In this chapter, we will discuss Memory Interfacing and IO Interfacing with 8085. The addressing mode in which the effective address of the memory location is written directly in the instruction. Encoded mode and Decoded mode. The high-order byte of the SR, the so-called It consists of three 8-bit bidirectional I/O ports (24I/O lines) which can be configured as per the requirement. 8086 Microprocessor Data Transfer Instructions. It stands for non-maskable interrupt and is available at pin 17. General Purpose Registers : The 8086 microprocessor has 8 registers each of 8 bits, AH, AL, BH, BL, CH, CL, DH, DL as shown below. DIV Used to divide the unsigned word by byte or unsigned double word by word. The destination operand can be any . Now, let us take a look at some program demonstrations using the above instructions . The syntax of this instruction is: MOV Destination, Source. Instruction register is 8-bit register just like every other register of microprocessor. This control signal enables the Read operation. It is compatible with almost all microprocessors. Size The microprocessor is of small size chip, hence is portable. By using this website, you agree with our Cookies Policy. Microprocessor consists of an ALU, register array, and a control unit. CS, DS, SS& ES. It is a 16-bit register used to store the memory address location of the next instruction to be executed. Multiprocessor means a multiple set of processors that executes instructions simultaneously. It stands for Minimum/Maximum and is available at pin 33. As the name suggests it controls the interrupts during a process. CX register It is referred to as counter. Enjoy unlimited access on 5500+ Hand Picked Quality Video Courses. 8085 is pronounced as "eighty-eighty-five" microprocessor. 8255A has three different operating modes . Zero flag This flag is set to 1 when the result of arithmetic or logical operation is zero else it is set to 0. It has a built-in pull-up resistor and is completely compatible with TTL circuits. MAR Register Memory Address Registers (MAR) are the complete version of MAR. It has a Program Counter (PC) register that stores the address of the next instruction based on the value of the PC, Microprocessor jumps from one location to another and takes decisions. The valid register pairs are AH and AL, BH and BL, CH and CL, and DH and DL. It stands for Hold Acknowledgement signal and is available at pin 30. A processor register (CPU register) is one of a small set of data holding places that are part of the computer processor. SHR Used to shift bits of a byte/word towards the right and put zero(S) in MSBs. Software interrupt In this type of interrupt, the programmer has to add the instructions into the program to execute the interrupt. Following is the table showing their status . These are 16 address/data bus. It can be disabled by resetting the microprocessor. Its power consumption is high because it has to control the entire system. Its content can be accessed by assembly programming. Write a program to exchange the data at 5000M& 6000M memory location. In Master mode, it is connected with HOLD input of the CPU. This unit controls the flow of data through the microprocessor. You can suggest the changes for now and it will be under the articles discussion tab. The programmer can read the contents of any of the three counters without disturbing the actual count in process. In this addressing mode, the offset address of the operand is given by the sum of contents of the BX/BP registers and 8-bit/16-bit displacement. Instruction pointer It is a 16-bit register used to hold the address of the next instruction to be executed. IMUL Used to multiply signed byte by byte/word by word. In our sample microprocessor, we have an address bus 8 bits wide and a data bus 8 bits wide. When this interrupt is executed, the processor saves the content of the PC register into the stack and branches to 003CH address. READY This signal indicates that the device is ready to send or receive data. It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions. This mode is similar to Mode 2 except the output remains low for half of the timer period and high for the other half of the period. REPE/REPZ Used to repeat the given instruction until CX = 0 or zero flag ZF = 1. Non-Vector interrupt In this type of interrupt, the interrupt address is not known to the processor so, the interrupt address needs to be sent externally by the device to perform interrupts. LAHF Used to load AH with the low byte of the flag register. Reads and writes of the same counter cannot be interleaved. We have tried to depict the architecture of 8085 with this following image , The following image depicts the pin diagram of 8085 Microprocessor , The pins of a 8085 microprocessor can be classified into seven groups . When this pin is set to low, it allows read/write operations, else this pin should be set to high. Each counter has 2 input pins, i.e. It indicates the current DMA cycle is the 128th cycle since the previous MARK output to the selected peripheral device. We can change the priority levels of the interrupts by changing the corresponding bit in the Interrupt Priority (IP) register as shown in the following figure. SAHF Used to store AH register to low byte of the flag register. There are various communication devices like the keyboard, mouse, printer, etc. It is a maskable interrupt, having the third highest priority among all interrupts. ALU performs arithmetical and logical operations on the data received from the memory or an input device. In the scanned sensor matrix mode, this unit acts as sensor RAM where its each row is loaded with the status of their corresponding row of sensors into the matrix. It is a 16-bit register that behaves like a flip-flop, i.e. I/O 8085 can address 2^8 = 256 I/O's, whereas 8086 can access 2^16 = 65,536 I/O's. For example, Intel 8096 is a 16-bit microcontroller. TRAP, RST7.5, RST6.5, RST5.5, INTA. Following is the list of 8085 pins used for interfacing with other devices . MUL Used to multiply unsigned byte by byte/word by word. Pin 30 This is EA pin which stands for External Access input. carry given by D3 bit to D4 is AF flag. PUSHA Used to put all the registers into the stack. AD7-AD0, it carries the least significant 8-bit address and data bus. NOT Used to invert each bit of a byte or word. Parity flag This flag is used to indicate the parity of the result, i.e. RISC microprocessor architecture uses highly-optimized set of instructions. When such an instruction is fetched from memory, it is directed to Instruction register. 1 I am currently studying the difference between microprocessors and microcontrollers and one of them says that: Microprocessors have less number of registers, so more operations are memory based. The following table differentiates the features of 8253 and 8254 , The most prominent features of 8253/54 are as follows . There are 5 interrupt signals, i.e. It is available in 3 versions based on the frequency of operation . SHL/SAL Used to shift bits of a byte/word towards left and put zero(S) in LSBs. Pin 31 This is ALE pin which stands for Address Latch Enable. Consequently, these are highly likely to have noise on their lines. Input pin Logic 1 is applied to a bit of the P register. In the Slave mode, it carries command words to 8257 and status word from 8257. It causes the processor to immediately terminate its present activity. In simple words, a Microprocessor is a digital device on a chip that can fetch instructions from memory, decode and execute them and give results. When the pulse goes high, it indicates address. The memory and I/O chips are connected to these buses; the CPU can exchange the desired data with the memory and I/O chips. In this port, functions are similar to other ports except that the logic 1 must be applied to appropriate bit of the P3 register. This signal is like wait state and is available at pin 23. JA/JNBE Used to jump if above/not below/equal instruction satisfies. The output is normally high after initialization. Addressing mode represents a method of assigning the address of the source of data or operand to the instruction given to the microprocessor. MOV Used to copy the byte or word from the provided source to the provided destination. A16-A19/S3-S6. Parallel Communication Interface In this type of communication, the interface gets a byte of data from the microprocessor and sends it bit by bit to the other systems in simultaneous (or) parallel fashion and vice-a-versa. AND Used for adding each bit in a byte/word with the corresponding bit in another byte/word. It is an 8-bit microcontroller. The keyboard consists of maximum 64 keys, which are interfaced with the CPU by using the key-codes. It is bidirectional, whereas address bus carries the location to where it should be stored and it is unidirectional. NMI and INTR. Embedded memory microcontroller This type of microcontroller is designed in such a way that the microcontroller has all programs and data memory, counters and timers, interrupts, I/O ports are embedded on the chip. If the overflow flag is reset then, the execution continues to the next instruction. New Microprocessors also perform operations on floating-point numbers also. If all 8 bits of a port are active, then the total current must be limited to 15mA (port P0: 26mA). Flag register value is pushed on to the stack. Following are the list of instructions under this group . This block is responsible for controlling the internal/external transfer of data/control/status word. The following table highlights the differences between a microprocessor and a microcontroller , Microcontrollers are divided into various categories based on memory, architecture, bits and instruction sets. It reduces the operational time by shortening the clock cycle per instruction. Clock Speed It determines the number of operations per second the processor can perform. It is an interrupt acknowledgement signal and id available at pin 24. AAS Used to adjust ASCII codes after subtraction. Each channel has 16-bit address and 14-bit counter. XOR Used to perform Exclusive-OR operation over each bit in a byte/word with the corresponding bit in another byte/word. CS, DS, SS& ES. This signal indicates the availability of a valid address on the address/data lines. It is used to write the data into the memory or the output device depending on the status of M/IO signal. 64-bit processor (64-bit computing) - A 64-bit processor refers to a microprocessor that can process data and instructions in chunks of 64 bits. 8051 microcontroller is designed by Intel in 1981. AX: This is the accumulator. For example, Intel 8031 and 8051 are 8 bits microcontroller. The general microcontroller consists of the processor, the memory (RAM, ROM, EPROM), Serial ports, peripherals (timers, counters), etc. The addressing mode in which the data operand is a part of the instruction itself is known as immediate addressing mode. it places an address on the address bus and memory responds by placing the data stored at the specifiedaddress on the data bus). Display Entry This mode allows the data to be entered for display either from the right side/left side. These lines are set to 0 when any key is pressed. Let us now discuss the functional parts of 8086 microprocessors. Both operands should be of same type either byte or a word. In the encoded mode, the counter provides the binary count that is to be externally decoded to provide the scan lines for the keyboard and display. Data Memory It stores the information to be processed. It has a 16-bit data bus, so it can read data from or write data to memory and ports either 16-bit or 8-bit at a time. If two interrupts of different priority levels are received simultaneously, the request of higher priority level is served. These instructions are used to execute the given instructions for number of times. Then the independent processor accesses the memory to execute the task. Input/Output (I/O) pin All the circuits within the microcontroller must be connected to one of its pins except P0 port because it does not have pull-up resistors built-in. Reads and writes of the same counter can be interleaved. Cost The cost of 8085 is low whereas that of 8086 is high. Instructions to transfer the instruction during an execution with some conditions . Interrupt are classified into following groups based on their parameter . The addressing modes of the 8086 microprocessor is classified as, Register and Immediate Data Addressing Modes, Data Memory Addressing Modes, The output remains LOW after the count value is loaded into the counter. It represents the result of the last arithmetic or logical instruction executed. The coprocessor uses QS0 & QS1 to track the status of the queue of the host processor. There are 5 interrupt signals, i.e. Copyright TUTORIALS POINT (INDIA) PRIVATE LIMITED. Later, it sends the result in binary to the output port. LSB to MSB and to Carry Flag [CF]. When it is low, it indicates the transfer of data. both share the same memory, I/O system bus, control logic, and control generator with the host processor. Pins 1 to 8 These pins are known as Port 1. LES Used to load ES register and other provided register from the memory. It is referred to the AX, BX, CX, and DX respectively. One instruction is required to support multiple addressing modes. It is 16-bit microprocessor 2. 8086 has eight general purpose registers. In the Polled mode, the CPU periodically reads an internal flag of 8279 to check whether any key is pressed or not with key pressure. The clock input is used to generate internal timings required by the microprocessor. X1, X2, CLK OUT. When GATE goes low, counting is terminated and the current count is latched till the GATE goes high again. There are 8 general purpose registers, i.e., AH, AL, BH, BL, CH, CL, DH, and DL. Interrupt is the method of creating a temporary halt during program execution and allows peripheral devices to access the microprocessor. Port A uses five signals from Port C as handshake signals for data transfer. When the external memory is used then the lower address byte (addresses A0A7) is applied on it, else all bits of this port are configured as input/output. i.e. Control flags controls the operations of the execution unit. Completes the current instruction that is in progress. SwathiDhanwada-MSFT 10,626. SCAS/SCASB/SCASW Used to scan a string and compare its byte with a byte in AL or string word with a word in AX. This Read/Write pin enables the data buffer to send/receive data over the data bus. In the encoded scan, an 88 keyboard or in the decoded scan, a 48 keyboard can be interfaced. The most prominent features of 8087 numeric data processor are as follows . Following is the table showing the list of Data-transfer instructions with their meanings. After the request is completed, the control goes back to the main program. You will be notified via email once the article is available for improvement. IP is loaded from the contents of the word location 00008H. 16-bit microcontroller This type of microcontroller is used to perform arithmetic and logical operations where higher accuracy and performance is required. The microprocessor follows a sequence: Fetch, Decode, and then Execute. A processor register is a quickly accessible location available to a computer's processor. Data bus carries the data to be stored. A register is a collection of flip-flops, Single bit digital data is stored using flip-flops. This article is being improved by another user right now. Areej June 3, 2020 Every modern processor includes multiple (very small) super-fast memory banks, called registers. A microprocessor can be classified into three categories . Following are the instructions under this group , CLC Used to clear/reset carry flag CF to 0. IN Used to read a byte or word from the provided port to the accumulator. By applying logic 0 to a port bit, the appropriate pin will be connected to ground (0V), and applying logic 1, the external output will keep on floating. There are 6 general purpose registers in 8085 processor, i.e. Serial Communication Interface In this type of communication, the interface gets a single byte of data from the microprocessor and sends it bit by bit to the other system serially and vice-a-versa. HLDA (HOLD Acknowledge) It indicates that the CPU has received the HOLD request and it will relinquish the bus in the next clock cycle. It is a specially designed microprocessor having a local memory of its own, which is used to control I/O devices with minimum CPU involvement. Port 0 The P0 (zero) port is characterized by two functions . RESET OUT This signal is used to reset all the connected devices when the microprocessor is reset. Some instructions specify registers as part of the instruction. There are two ways of communication in which the microprocessor can connect with the outside world. Its frequency is different for different versions, i.e. None of the instructions are used for communication, like WAIT, ESC, etc. We do not have any 128-bit Microprocessor at work at present one of the reasons for this is that we are a long way from exhausting the 64-bit address space itself, we use it at a constant rate of roughly 2 bits every 3 years. The Status Register, or SR, is 16 bits (2 bytes) wide. When this interrupt is activated, these actions take place . AAA Used to adjust ASCII after addition. EU and BIU are connected with the Internal Bus. This process is performed by a circuit called an analogue to digital converter, A to D converter or ADC. It is the power signal which is required for the operation of the circuit. The code of key pressed with SHIFT and CONTROL status is stored into the FIFO RAM. 8087 Architecture is divided into two groups, i.e., Control Unit (CU) and Numeric Extension Unit (NEU). Size 8085 is 8-bit microprocessor, whereas 8086 is 16-bit microprocessor. Once the instructions are identified by the 8086/8088 processor, then it is allotted to the 8087 co-processor for further execution. 1. It is connected to internal data bus & ALU. After completion of the task, it sends an acknowledgement to the host processor by using the status signal or an interrupt request. It is used to enable/disable the external memory interfacing. It is available at pin 34 and used to indicate the transfer of data using data bus D8-D15. 8087 numeric data processor is also known as Math co-processor, Numeric processor extension and Floating point unit. RCL Used to rotate bits of byte/word towards the left, i.e. Following are the timing and control signals, which control external and internal circuits . In the master mode, they are the four least significant memory address output lines generated by 8257. It is available at pin 21 and is used to restart the execution. A few CPUs also place special registers such as the PC and the status register in the register file. ALE It is a positive going pulse generated when a new operation is started by the microprocessor. When this signal is active, it indicates to the other processors not to ask the CPU to leave the system bus. When this signal is high, then the processor has to wait for IDLE state, else the execution continues. The timing and control unit handles the timings for the operation of the circuit. The system bus consists of an 8-bit data bus, a 16-bit address bus and bus control signals. The pins A0, RD, and WR are used for command, status or data read/write operations. It is an 8-bit register having five 1-bit flip-flops, which holds either 0 or 1 depending upon the result stored in the accumulator. MSB to LSB and to Carry Flag [CF]. CS value of the return address and IP value of the return address are pushed on to the stack. The system bus is controlled by the coprocessor and the host processor independently. Fetch Stage and Execute Stage, which improves performance. Now the CPU is in HOLD state and the DMA controller has to manage the operations over buses between the CPU, memory, and I/O devices. Based on the instruction set configuration, the microcontroller is further divided into two categories. CS It stands for Code Segment. It is used to read a signal from the external program memory. Word Length It depends upon the width of internal data bus, registers, ALU, etc. For example: RST7.5, RST6.5, RST5.5. Inputs and outputs are latched. RD This signal indicates that the selected IO or memory device is to be read and is ready for accepting data available on the data bus. A register serves as a quick memory for accepting, storing, and sending data and instructions that the CPU will need right away. It is an 8-bit register. 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It is an interrupt request signal, which is sampled during the last clock cycle of each instruction to determine if the processor considered this as an interrupt or not. In the early 1970s the introduction of large-scale . The architecture of 8087 coprocessor is as follows , Let us first take a look at the pin diagram of 8087 , The following list provides the Pin Description of 8087 . This signal acknowledges the HOLD signal. it changes its status according to the result stored in the accumulator. Extra segment (ES) It is used to store operands for arithmetic operations. Data in microprocessors can move from one location to another. It has 8 register stack, which holds the operands for instructions and their results. Ports do not have interrupt capability. LSB to CF and CF to MSB. The coprocessor shares the same memory, IO system, bus, control logic and clock generator. There are 8 different addressing modes in 8086 programming . It is an active-low bidirectional tri-state input line, which is used by the CPU to read internal registers of 8257 in the Slave mode. It is set to 1 for interrupt enabled condition and set to 0 for interrupt disabled condition. Communication between the host and the independent processor is done through memory space. 8085 consists of the following functional units . Instruction Set It is the set of instructions that the microprocessor can understand. In the master mode, it is used to load the data to the peripheral devices during DMA memory read cycle. OUTS/OUTSB/OUTSW Used as an output string/byte/word from the provided memory location to the I/O port. Let us now discuss these instruction sets in detail. The data from these lines is synchronized with the scan lines to scan the display and the keyboard. If all ports (32 bits) are active, then the total maximum current must be limited to 71mA. It stands for Data Enable and is available at pin 26. Interrupts are the signals generated by external devices to request the microprocessor to perform a task. It is available at pin 28. The compiler also has to work more to convert high-level language instructions into machine code. 8086 Microprocessor is divided into two functional units, i.e., EU (Execution Unit) and BIU (Bus Interface Unit). The first 0 means INTA informs the external device to get ready and during the second 0 the microprocessor receives the 8 bit, say X, from the programmable interrupt controller. Register plays a major role in CPU operations. It is enabled only when D is low. when the result of the operation is negative, then the sign flag is set to 1 else set to 0. . RESET IN This signal is used to reset the microprocessor by setting the program counter to zero. It is designed by Intel to transfer data at the fastest rate. Temperature sensing and controlling devices like microwave oven, chimneys. Their conditions are shown in the following table , These are the status signals that provide the status of operation, which is used by the Bus Controller 8288 to generate memory & I/O control signals. Its architecture is designed to decrease the memory cost because more storage is needed in larger programs resulting in higher memory cost. Bandwidth It is the number of bits processed in a single instruction. IP value is loaded from the contents of word location X 4. Memory Data Registers (MDR): It contains data to be written into or to be read out from the addressed location. . It is used to transfer the data & Address I/O devices. It is available at pin 31. The 8086 has two hardware interrupt pins, i.e. Scanned Keyboard Mode In this mode, the key matrix can be interfaced using either encoded or decoded scans. In this addressing mode, the operands offset is computed by adding the base register contents. If it is set, then the program can be run in a single step mode. XCHG Used to exchange the data from two locations. IDIV Used to divide the signed word by byte or signed double word by word. It allows the user to insert a single instruction as an alternative to many simple instructions. Each of the processors have their own local bus to access the local memory/I/O devices. It is an 8-bit register used to perform arithmetic, logical, I/O & LOAD/STORE operations. HOLD This signal indicates that another master is requesting the use of the address and data buses. AAM Used to adjust ASCII codes after multiplication. All other devices like program memory, ports, data memory, serial interface, interrupt control, timers, and the CPU are all interfaced together through the system bus. What is data register in microprocessor? The register file is the component that contains all the general purpose registers of the microprocessor. INTA It is an interrupt acknowledgment signal. HLDA is set to low after the HOLD signal is removed. Data segment (DS) Data segment is a 16-bit register containing address of 64KB segment with program data. It is used in portable devices like Apple iPod due to its power efficiency. The interrupts from Type 5 to Type 31 are reserved for other advanced microprocessors, and interrupts from 32 to Type 255 are available for hardware and software interrupts. INTO Used to interrupt the program during execution if OF = 1, IRET Used to return from interrupt service to the main program. A small program or a routine that when executed, services the corresponding interrupting source is called an ISR. The Keyboard can be interfaced either in the interrupt or the polled mode. The remaining three signals from Port C can be used either as simple I/O or as handshake for port B. TYPE 2 interrupt represents non-maskable NMI interrupt. It utilizes simple addressing modes and fixed length instructions for pipelining. For example: MVI K, 20F: means 20F is copied into register K. In this mode, the data is copied from one register to another. The keyboard first scans the keyboard and identifies if any key has been pressed. SUB Used to subtract the byte from byte/word from word. One more interrupt pin associated is INTA called interrupt acknowledge. As the name suggests, it performs arithmetic and logical operations like Addition, Subtraction, AND, OR, etc. It stands for address enable latch and is available at pin 25. The output FE transistor is turned off and the other pin remains connected to the power supply voltage over a pull-up resistor of high resistance. Let us now discuss in detail the pin configuration of a 8086 Microprocessor. POPF Used to copy a word at the top of the stack to the flag register. Hardware interrupt is caused by any peripheral device by sending a signal through a specified pin to the microprocessor. Flag register values are pushed on to the stack. Register array consists of registers identified by letters like B, C, D, E, H, L and accumulator. $\overline{BHE}$/S7 During the first clock cycle, the $\overline{BHE}$/S7 is used to enable data on to the higher byte of the 8086 data bus and after that works as status line S7. It includes 5 signals, i.e. This signal indicates to the processor that external devices are requesting to access the address/data buses. 8-bit microcontroller This type of microcontroller is used to execute arithmetic and logical operations like addition, subtraction, multiplication division, etc. Address Bus 8085 has 16-bit address bus while 8086 has 20-bit address bus. Each port uses three lines from port C as handshake signals. It is an active low bi-direction tri-state line, which is used to load the contents of the data bus to the 8-bit mode register or upper/lower byte of a 16-bit DMA address register or terminal count register. The register file is the component that contains all the general purpose registers of the microprocessor. All Rights Reserved. The 8086 and 8088 can perform most of the operations but their instruction set is not able to perform complex mathematical operations, so in these cases the microprocessor requires the math coprocessor like Intel 8087 math coprocessor, which can easily perform these operations very quickly. Its execution includes the following steps . The most prominent features of a 8086 microprocessor are as follows . There are 3 clock signals, i.e. Each counter has two input signals - CLOCK & GATE, and one output signal - OUT. Following is the list of instructions under this group , LOOP Used to loop a group of instructions until the condition satisfies, i.e., CX = 0, LOOPE/LOOPZ Used to loop a group of instructions till it satisfies ZF = 1 & CX = 0, LOOPNE/LOOPNZ Used to loop a group of instructions till it satisfies ZF = 0 & CX = 0, JCXZ Used to jump to the provided address if CX = 0. This is commonly described in the hexadecimal notation we've been using. Few of the special processors are briefly discussed . D4 D7), then this flag is set, i.e. Pins of this port occupy addresses intended for the external memory chip. LODS/LODSB/LODSW Used to store the string byte into AL or string word into AX. Non-Maskable interrupt In this type of interrupt, we cannot disable the interrupt by writing some instructions into the program. AAD Used to adjust ASCII codes after division. EA register is set to one for enabling interrupts and set to 0 for disabling the interrupts. When INTR signal goes high, the following events can occur . The numeric extension unit handles all the numeric processor instructions like arithmetic, logical, transcendental, and data transfer instructions. Maximum mode and Minimum mode. TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. When these pins are configured as inputs (i.e. CS is loaded from the contents of the next word location 0000AH. XLAT Used to translate a byte in AL using a table in the memory. RQ/GT1 & RQ/GT0 These are the Request/Grant signals used by the 8087 processors to gain control of the bus from the host processor 8086/8088 for operand transfers. Let us take a look at the programming of 8085 Microprocessor. These signals provide the status of instruction queue. Note NTA is not an interrupt, it is used by the microprocessor for sending acknowledgement. It holds the addresses of instructions and data in memory, which are used by the processor to access memory locations. RD, WR, CS, and the address lines A0 & A1. 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