Computer Architecture: Questions on Intel 8085 Microprocessor

Topics: X86, Central processing unit, Processor register Pages: 8 (1935 words) Published: February 5, 2014
Darcy M. Ablir

1. Briefly explain the history of 8085 Microprocessor

INTEL 8085 (eighty-eighty five) is an 8 bit microprocessor introduced by Von Neumann of Intel in 1977. It was a binary compatible with its processor Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microprocessor. The development of an 8085 comes with the addition of “5” from its predecessor of Intel 8080. The 5 means that the system of 8085 only requires a +5 volts supply only rather than the 8080’s system which requires +5, -5, and 12volts respectively.

(Intel 8085 MicroArchitecture )

2. Explain the meaning of 8085 Microprocessor

Intel 8085 is an 8-bit microprocessor developed by Intel in 1977. It uses a total of 246 patterns with 74 instructions only. Since these instructions have multiple different formats. It is capable of addressing 64K memory, has 40 pins, requires +5 volts supply, and can operate in 3 Mhz clock.

3. What are the various registers of 8085. Discuss the function.

One 8-bit Accumulator (ACC) also known as Register A.
The Accumulator is an 8-bit register associated with the ALU. The register “A” in the 8085 is an accumulator. It is used to hold one of the operands of an arithmetic or logical operation. It serves as one input to the ALU. The other operand for an arithmetic or logical operation may be stored either in the memory or in one of the general-purpose registers. The final results of an arithmetic or logical operation is placed in the accumulator. Six 8-bit general purpose registers. The B, C, D, E, H, and L. The 8085 microprocessor contains six 8-bit general purpose registers. They are: B, C, D, E, H and L register. To hold 16 bit data a combination of two 8-bit register can be employed. The combination of two 8-bit registers is known as ‘REGISTER PAIR”. The valid register pairs in the 8085 are B-C, D-E and H-L. The programmer can not form a register pair by selecting any two registers of his choice. The H-L pair is used to act as memory pointer and for this purpose it holds the 16-bit address of a memory location. The general-purpose registers and the accumulator are accessible to programmer. He can store data in these registers during writing his program. One 16-Bit Stack Pointer (SP)

It is a 16-bit special function register. The STACK is a sequence of memory location set aside by a programmer to store/retrieve the contents of accumulator, flags, program counter and general purpose registers during the execution of a program. Since the stack works on LIFO (LAST IN FIRST OUT) principle, its operation is faster compared normal store/retrieve of memory locations. During the execution of a program sometimes it becomes necessary to save the contents of some registers which is needed for some other operations the content which were save the contents of some registers which are needed for some other operations in the subsequent steps of the program. The content of such registers are save in the stack. Then the registers are used for some other operations. After completing the needed operations the contents which were saved in the stack are brought back to the registers. The contents of only those registers are saved, which are needed in the later part of the program. The stack pointer (SP) controls addressing of the stack. The SP holds the address of the top element of data stored in the stack. One 16-bit Program Computer (PC)

It is a 16-bit special purpose register. It is used to hold the memory address of the next instruction to be executed. It keeps the track of memory addresses of the instruction in a program while they are being executed. The microprocessor increments the content of the program counter during the execution of an instruction so that it points to the address of the next instruction in the program at the end of the execution of an instruction Instruction Register

The instruction register holds the op code (operation...
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