Apr 09, 2017 8085 is a second generation 8 bit microprocessor and is the base for studying and using all the modern microprocessors available in the market. The zero status flag z is set to 1 if the result of an arithmetic or logical operation is zero. However, in our 8085 instruction set does not provide any instruction, which explicitly uses the ac flag. There is one flag registers which contain number of flags what is a flag. Press key alt, 0af, display will show the content of user accumulator and flag register.
Lecture note on microprocessor and microcontroller theory and. Also learn about carry flag, auxiliary carry flag and their differences along. In 8085 microprocessor, flag register basically consists of 8 bits and. Flag register is a group of flip flops used to give status of different operations result. When an operation is performed by alu the result is transferred on data bus and status of result will be stored in flip flops. Control and status signal in 8085 8085 microprocessor. For example the zero flag zf will set if the result of execution of an instruction is zero. The functional components of a cpu are arithmetic logic unit alu, control and timing units, registers are found in a single integrated circuit called ic. The entire group of instructions that a microprocessor supports is called instruction set. In 8085 microprocessor, flag register consists of 8 bits and only 5 of them are useful. In this video, i have explained flag register of 8085 by following outlines. The status of the result is indicated by the flag bits of the flag register.
Instructions performing actions in assembly language are called a imperative. What are the functions of flag registers in 8086 microprocessor. Therefore they are also called as status register and psw program status word. Auxiliary carry flag 1 point the interrupt in an 8085 microprocessor that is not affected by the value of the interrupt enable ie flip flop is trap rst 7.
Define the function of parity flag and zero flag in 8085. The 8085 machine language the 8085 from intel is an 8bit microprocessor. A microprocessor which has n data lines is called an nbit microprocessor i. The internal architecture of 8085 includes the alu, timing and control unit, instruction register and decoder, register array, interrupt control and serial io control. Flag register of 8086 microprocessor geeksforgeeks. The 8085 includes six registers, one accumulator and one flag register, as shown in fig. Also learn about why the flags in microprocessor are called as flags. Learn in detail about the architecture of 8085 microprocessor. Each instruction is represented by an 8bit binary value. The auxiliary carry status flag holds carry out of bit 3 to 4 resulting from the execution of an arithmetic operation. Flags flags are flipflops that store bit 0 or 1 based on the arithmetic or logical operation performed by an arithmetic and logical unit alu. Carry flag cy, auxiliary carry flag ac, parity flag p, zero flag z and sign flag s7. The time for the back cycle of the intel 8085 a2 is 200 ns. In 8085, 5 flags are definite at the definite bit of flag register.
Intel 8085 8bit microprocessor shrimati indira gandhi. Explain briefly the flag register in the 8085 microprocessor. Auxiliary carry flag 1 point the interrupt in an 8085 microprocessor that is not affected by the value of the interrupt enable ie flip flop is. It is a 40 pin c package fabricated on a single lsi chip. Tutorial on introduction to 8085 architecture and programming. This allows instructions following to act accordingly, such as a branch as a result of two values comparing equal.
The 8085 has six generalpurpose registers to store 8bit data. Loosely coupled configuration has shared system bus, system memory, and system io. Flag register of 8085 microprocessor is explained using proper example. In most of the operations, the result is stored in the accumulator. When a call is executed, the 8086 automatically pushes the current value of cs and ip onto the stack. The 8085 microprocessor kit is a lowcost single board computer designed for. The content of the memory location, whose address is one. A flag is a flipflop which indicates some condition which arises after execution of an arithmetic or logical instruction. Flag register in 8085 microprocessor geeksforgeeks. The intel 8085 eightyeightyfive is an 8bit microprocessor produced by intel and introduced in march 1976.
There are five flags present in 8085 microprocessor. Here this video is a part of microprocessor and interfacing 8085. In this article you will get to know about the definition, architecture, block diagram and working of. The 8085 8080aprogramming model includes six registers, one accumulator, and one flag register, as shown in figure.
The reason for the difference is that some actually most instructions have multiple different formats. Introduction fundamentals of microprocessor 8085 and. Flags, interrupts, instruction register and decoders,arithmetic and logic unit and various other units explained in detail. Over view of microprocessor 8085 and its application. What are the different flags in 8085 answer abhijit.
List the control and status signals of 8085 and mention its need. In case there exist a carry from the addition or borrow from the subtraction or the comparison, carry flag cs is set to 1. This instruction will set the value of parity flag to 1 as the bcd code of. Flag register of 8085 microprocessor with example 8085 auxiliary. It is an nmos device having around 6200 transistors contained in a 40 pin dip package. When microprocessor receives interrupt signal, it discontinues whatever it was executing. Intel 8085 8bit microprocessor intel 8085 is an 8bit, nmos microprocessor. When set flag termed as set is in position 1 and in 0 position it is termed as reset. Accumulator is an 8 bit register which stores data and performs arithmetic and logical operations. The sign status flag is set to 1 if the most significant bit of the result of an arithmetic or logical operation is 1 otherwise 0.
It indicates some condition produced by the execution of an instruction. It is a softwarebinary compatible with the morefamous intel 8080 with only two minor instructions added to support its added interrupt and serial inputoutput features. Any module could be a processor capable of being a bus. These three status lines serve to indicate the general status of the processor with. The respective bit flags up goes to 1 when the condition for the flag has occurred. Central processing unit cpu is carved on a single chip is called a microprocessor. A nice feature, singlestep running, helps students learn the. What is the technology used in the manufacture of 8085. The flag register in 8085 is an 8bit register which contains 5 bit positions. In 8085 microprocessor, the value of the most significant bit of the result following the execution of any arithmetic or boolean instruction is stored in the.
But 8085 microprocessor still stores this ac information in bit position 4 of the flags register. May2012 parity flag parity is defined by the number of one. The 8085 microprocessor kit is a lowcost single board computer designed for selflearning the popular 8085 microprocessor. The instruction loads eight bits in the accumulator with the following interpretations. The result of the operation is stored in the accumulator.
Following status flags have been offered within the intel 8085. What is meant by the statement that 8085 is a 8bit microprocessor. Its data bus width is 8bit and address bus width is 16bit, thus it can address 216 64 kb of memory. This allows instructions following to act accordingly, such as a branch as. Flag register in 8085 is a one byte register used to store 5 flags. Explain flag register of 8085 microprocessor ques10. All the flags are present in an 8bit register called as status. For sign flag if the result of an msb operation is 1 then it is set else it is reset. This instruction will set the parity flag to 1 as the bcd code of 05h is 00000101, which contains even number of ones i.
Status or flag register in 8085 microprocessor electricalvoice. A carry status flag b auxiliary carry status flag c sign status flag d zero status flag. Flags are flipflops that store bit 0 or 1 based on the arithmetic or logical operation performed by an arithmetic and logical unit alu. The result of execution of daa instruction, is affected by the status of this flag. The architecture of 8085 consists of three main sections, alu arithmetic and logical unit, timing and control unit and registers shown in the following figure. In addition to the above mentioned regiter the 8085 microprocessor contains a set of five flipflops which serve as flag or status flags. Interview questions on microprocessor with detailed answers. Jan 07, 2009 flag register the status flags of the 8080 and 8085 are single bits which indicate the logical conditions that existed as a result of the execution of the instruction just completed. Scribd is the worlds largest social reading and publishing site. All the flags are present in an 8bit register called as status register or flags register. Jan 07, 2009 interfacing the 8085 a brief description of the signals between the 8085 and the outside world follows. Internal architecture of 8085 microprocessor learn about. The kit enables studying from low level programming with direct machine code entering to high level programming with pc tools easily.
Flag register of 8085 microprocessor with example 8085. Interfacing the 8085 interfacing the 8085 a brief description of the signals between the 8085 and the outside world follows. The 8085 uses a total of 246 bit patterns to form its instruction set. They show the status conditions after any arithmetic and logical operation. The flags generally reflect the status of arithmetic or logical operations. Appreciate the detailed explanation about 8085 architecture. Refer to the reference manual for pinouts and details. The intel 8085 microprocessor contains five the flipflops are set or reset according to the conditions which arises during an arithmetic or logical operation. Mar 05, 2018 flags flags are flipflops that store bit 0 or 1 based on the arithmetic or logical operation performed by an arithmetic and logical unit alu. Instruction set of 8085 an instruction is a binary pattern designed inside a microprocessor to perform a specific function. We will also take a look at the examples where flag bits are affected. Carry flag cy, auxiliary carry flag ac, parity flag p, zero flag z. Dec2012 ale address latch enable and read and write io, s0 s1 ready 9. Figure below shows the details of the 16 bit flag register of 8086 cpu.
Feb 28, 2019 but 8085 microprocessor still stores this ac information in bit position 4 of the flags register. The flag register of 8085 microprocessor consists of 5 flags. Prerequisite registers of 8085 microprocessor the flag register is a special purpose register. The 8085 8080a has six generalpurpose registers to store 8bit data. Nov 03, 2017 flag register of 8085 microprocessor is explained using proper example. Lecture note on microprocessor and microcontroller theory. Ale can also be used to strobe the status information. These five flags are of 1bit ff and are known as zero, sign, carry, parity and auxiliary carry. This is a multipurpose instruction used to read the status of interrupts 7. Sign flag carry flag auxiliary carry flag zero flag no, the answer is incorrect. When the signal on this pin is low, selected memory on input output device is read and the information is placed on the data bus. The stack the stack is used for temporary storage of information such as data or addresses. Depending upon the value of result after any arithmetic and logical operation the flag bits become set 1 or reset 0.
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