8055 MICROPROCESSOR PDF

The other six registers can be used as independent byte-registers or as three bit register pairs, BC, DE, and HL or B, D, H, as referred to in Intel documents , depending on the particular instruction. Some instructions use HL as a limited bit accumulator. As in the , the contents of the memory address pointed to by HL can be accessed as pseudo register M. The accumulator stores the results of arithmetic and logical operations, and the flags register bits sign, zero, auxiliary carry, parity, and carry flags are set or cleared according to the results of these operations.

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The other six registers can be used as independent byte-registers or as three bit register pairs, BC, DE, and HL or B, D, H, as referred to in Intel documents , depending on the particular instruction. Some instructions use HL as a limited bit accumulator. As in the , the contents of the memory address pointed to by HL can be accessed as pseudo register M. The accumulator stores the results of arithmetic and logical operations, and the flags register bits sign, zero, auxiliary carry, parity, and carry flags are set or cleared according to the results of these operations.

The sign flag is set if the result has a negative sign i. The auxiliary or half carry flag is set if a carry-over from bit 3 to bit 4 occurred. The parity flag is set according to the parity odd or even of the accumulator. The zero flag is set if the result of the operation was 0. Lastly, the carry flag is set if a carry-over from bit 7 of the accumulator the MSB occurred. Some of them are followed by one or two bytes of data, which can be an immediate operand, a memory address, or a port number.

A NOP "no operation" instruction exists, but does not modify any of the registers or flags. Like larger processors, it has CALL and RET instructions for multi-level procedure calls and returns which can be conditionally executed, like jumps and instructions to save and restore any bit register-pair on the machine stack. There are also eight one-byte call instructions RST for subroutines located at the fixed addresses 00h, 08h, 10h, These are intended to be supplied by external hardware in order to invoke a corresponding interrupt-service routine, but are also often employed as fast system calls.

One sophisticated instruction is XTHL, which is used for exchanging the register pair HL with the value stored at the address indicated by the stack pointer. For two-operand 8-bit operations, the other operand can be either an immediate value, another 8-bit register, or a memory cell addressed by the bit register pair HL. The only 8-bit ALU operations that can have a destination other than the accumulator are the unary incrementation or decrementation instructions, which can operate on any 8-bit register or on memory addressed by HL, as for two-operand 8-bit operations.

Direct copying is supported between any two 8-bit registers and between any 8-bit register and a HL-addressed memory cell, using the MOV instruction. An immediate value can also be moved into any of the foregoing destinations, using the MVI instruction. Due to the regular encoding of the MOV instruction using nearly a quarter of the entire opcode space there are redundant codes to copy a register into itself MOV B,B, for instance , which are of little use, except for delays.

Adding HL to itself performs a bit arithmetical left shift with one instruction. Adding the stack pointer to HL is useful for indexing variables in recursive stack frames. Subtraction and bitwise logical operations on 16 bits is done in 8-bit steps. Operations that have to be implemented by program code subroutine libraries include comparisons of signed integers as well as multiplication and division. Undocumented instructions[ edit ] A number of undocumented instructions and flags were discovered by two software engineers, Wolfgang Dehnhardt and Villy M.

Sorensen in the process of developing an assembler. These instructions use bit operands and include indirect loading and storing of a word, a subtraction, a shift, a rotate, and offset operations. Development system[ edit ] Intel produced a series of development systems for the and , known as the MDS Microprocessor System. The original development system had an processor.

Later and support was added including ICE in-circuit emulators. It is a large and heavy desktop box, about a 20" cube in the Intel corporate blue color which includes a CPU, monitor, and a single 8-inch floppy disk drive. Later an external box was made available with two more floppy drives.

This unit uses the Multibus card cage which was intended just for the development system. A surprising number of spare card cages and processors were being sold, leading to the development of the Multibus as a separate product. The later iPDS is a portable unit, about 8" x 16" x 20", with a handle.

It can also accept a second processor, allowing a limited form of multi-processor operation where both processors run simultaneously and independently.

The screen and keyboard can be switched between them, allowing programs to be assembled on one processor large programs took awhile while files are edited in the other. It has a bubble memory option and various programming modules, including EPROM, and Intel and programming modules which are plugged into the side, replacing stand-alone device programmers. All data, control, and address signals are available on dual pin headers, and a large prototyping area is provided.

List of Intel [ edit ] Model Number.

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Intel 8085

Accumulator aids in storing two quantities. The data to be processed by arithmetic and logic unit is stored in accumulator. It also stores the result of the operation carried out by the Arithmetic and Logic unit. The accumulator is also called an 8-bit register. The accumulator can be used to send or receive data from the Internal Data bus. So there is a necessity for creating a separate unit which can perform such types of operations.

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8055 MICROPROCESSOR PDF

Vugal Which indicate that the selected IO or Memory device is to be read and data is available on the data bus. The contents of register H are exchanged with the contents of microprocexsor D, and the contents of register L are exchanged with the contents of register E. Sorensen in the process of developing an assembler. This is provided by CLK pin. Pin Diagram and Pin description of Microprocessor The contents of the accumulator are copied into the memory location specified by the operand. Week 7 Aug 20 35 upvotes. Consider we have an address to be processed.

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8085 Microprocessor Architecture Explained

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