The Intel " eighty-eighty-five " is an 8-bit microprocessor produced by Intel and introduced in March However, it requires less support circuitry, allowing simpler and less expensive microcomputer systems to be built. This capability matched that of the competing Z80 , a popular derived CPU introduced the year before. The is supplied in a pin DIP package. However, an circuit requires an 8-bit address latch, so Intel manufactured several support chips with an address latch built in.
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The Intel " eighty-eighty-five " is an 8-bit microprocessor produced by Intel and introduced in March However, it requires less support circuitry, allowing simpler and less expensive microcomputer systems to be built. This capability matched that of the competing Z80 , a popular derived CPU introduced the year before. The is supplied in a pin DIP package.
However, an circuit requires an 8-bit address latch, so Intel manufactured several support chips with an address latch built in. Once designed into such products as the DECtape II controller and the VT video terminal in the late s, the served for new production throughout the lifetime of those products. This was typically longer than the product life of desktop computers. The is a conventional von Neumann design based on the Intel Unlike the it does not multiplex state signals onto the data bus, but the 8-bit data bus is instead multiplexed with the lower 8-bits of the bit address bus to limit the number of pins to State signals are provided by dedicated bus control signal pins and two dedicated bus state ID pins named S0 and S1.
Pin 39 is used as the Hold pin. Only a single 5 volt power supply is needed, like competing processors and unlike the The uses approximately 6, transistors. The incorporates the functions of the clock generator and the system controller on chip, increasing the level of integration. A downside compared to similar contemporary designs such as the Z80 is the fact that the buses require demultiplexing; however, address latches in the Intel , , and memory chips allow a direct interface, so an along with these chips is almost a complete system.
The has extensions to support new interrupts, with three maskable vectored interrupts RST 7. Each of these five interrupts has a separate pin on the processor, a feature which permits simple systems to avoid the cost of a separate interrupt controller. The RST 7. All interrupts are enabled by the EI instruction and disabled by the DI instruction.
All three are masked after a normal CPU reset. SIM and RIM also allow the global interrupt mask state and the three independent RST interrupt mask states to be read, the pending-interrupt states of those same three interrupts to be read, the RST 7.
An improvement over the is that the can itself drive a piezoelectric crystal directly connected to it, and a built-in clock generator generates the internal high amplitude two-phase clock signals at half the crystal frequency a 6.
The internal clock is available on an output pin, to drive peripheral devices or other CPUs in lock-step synchrony with the CPU from which the signal is output. The can also be clocked by an external oscillator making it feasible to use the in synchronous multi-processor systems using a system-wide common clock for all CPUs, or to synchronize the CPU to an external time reference such as that from a video source or a high-precision time reference.
The is a binary compatible follow up on the Exceptions include timing-critical code and code that is sensitive to the aforementioned difference in the AC flag setting or differences in undocumented CPU behavior. The same is not true of the Z 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. It also has a bit program counter and a bit stack pointer to memory replacing the 's internal stack.
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. As in many other 8-bit processors, all instructions are encoded in a single byte including register-numbers, but excluding immediate data , for simplicity. 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. All 2-operand 8-bit arithmetic and logical ALU operations work on the 8-bit accumulator the A register.
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.
Although the is an 8-bit processor, it has some bit operations. 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. 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. 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. These instructions are written in the form of a program which is used to perform various operations such as branching, addition, subtraction, bitwise logical , and bit shift operations. More complex operations and other arithmetic operations must be implemented in software.
For example, multiplication is implemented using a multiplication algorithm. Pro-Log Corp. The product was a direct competitor to Intel's Multibus card offerings. OKI M80C The CPU is one part of a family of chips developed by Intel, for building a complete system.
Many of these support chips were also used with other processors. In many engineering schools   the processor is used in introductory microprocessor courses.
Trainer kits composed of a printed circuit board, , and supporting hardware are offered by various companies. These kits usually include complete documentation allowing a student to go from soldering to assembly language programming in a single course. Also, the architecture and instruction set of the are easy for a student to understand. Shared Project versions of educational and hobby based single board computers are noted below in the External Links section of this article. Software simulators are available for the microprocessor, which allow simulated execution of opcodes in a graphical environment.
From Wikipedia, the free encyclopedia. Intel and several others. AMD Am Mitsubishi M5L At the time of release, it is available in samples then full production in first quarter of Since use of these instructions usually relates to specific hardware features, the necessary program modification would typically be nontrivial.
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Opcode Sheet for 8085 Microprocessor With Description
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Number of instructions in 8085 Microprocessor