SILICON GATE MOS 8080 A

INSTRUCTION SET

The accumulator group instructions include arithmetic and logical operators with direct, indirect, and immediate ad- dressing modes.

Move, load, and· store instruction groups provide the ability to move either a or 16 bits of data between memory,' the six working registers and the accumulator using direct, in- direct, and 'immediate addressing modes.

The ability to branch to different portions of the program is provided with jump, jump conditional, and computed jumps. Also the ability to call to and return from sub- routines is provided both conditionally and unconditionally. The RESTART (or single byte call instruction) is useful for interrupt vector operation.

OOl:Jble precision operators such as stack manipulation and double add instructions extend both the arithmetic and interrupt handl ing capability of the a080A. The ability to

increment and decrement memory, the six general registers and the accumulator is provided as well as extended incre- ment and decrement instructions to operate on the register pairs and stack pointer. Further capability is provided by the abil ity to rotate the accu mu lator I~ft or right through or arou nd the carry bit.

Input and output may be accomplished using memory ad- dresses as I/O ports or the directly addressed I/O provided for in the 8080A instruction set.

The following special instruction group completes the 8080A instruction set: the NOP instruction, HALT to stop pro- cessor execution and the OAA instructions provide decimal arithmetic capabil ity. STC allows the carry flag to be di- rectly set, and the CMC instruction allows it to be comple- mented. CMA complements the contents of the accumulator and XCHG exchanges the contents of two 16-bit register pairs directly.

Data and Instruction Formats

Data in the a080A is stored in the form of a-bit binary integers. All data transfers to the system data bus will be in the same format.

1 0 7 06 Os 04 03 02 01 001

OATA WORO

The program instructions may be one, two, or three bytes in length. Multiple byte instructions must be stored in successive words in program memory. The instruction formats then depend on the particular operation executed.

One Byte Instructions

TYPICAL INSTRUCTIONS

Register to register, memory refer- ence, arithmetic or logical, rotate, return, push, pop, enable or disable Interrupt instructions

Two Byte Instructions

10 .7 06 Os D4 °3 °2 °1 DO I OP CODE

10 7 °6 Os D4 °3 °2 °1 DO I OPERANO

Three Byte Instructions

 

DO I OP COOE

10 7

°6

Os

04

°3

°2

°1

10 7

°6

Os

04

°3

°2

0 1

DO I LOW ADDRESS OR OPERAND 1

1 0 7

06

Os

04

03

°2

°1

DO I HIGH ADDRESS OR OPERANO 2

Immediate mode or I/O instructions

Jump, call or direct load and store instructions

For the 8080A a logic "1" is defined as a high level and a logic 110" is defined as a low level.

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Intel 8080 manual Instruction SET, Typical Instructions
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8080 specifications

The Intel 8085 and 8080 microprocessors were groundbreaking innovations in the world of computing, paving the way for future microprocessor development and personal computing.

The Intel 8080, introduced in 1974, was an 8-bit microprocessor that played a fundamental role in the early days of personal computing. With a 16-bit address bus, it had the capability to address 64 KB of memory. Running at clock speeds of 2 MHz, the 8080 was notable for its instruction set, which included 78 instructions and 246 opcodes. It supported a range of addressing modes including direct, indirect, and register addressing. The 8080 was compatible with a variety of peripherals and played a crucial role in the development of many early computers.

The microprocessor's architecture was based on a simple and efficient design, making it accessible for hobbyists and engineers alike. It included an 8-bit accumulator, which allowed for data manipulation and storage during processing. Additionally, the 8080 featured registers like the program counter and stack pointer, which facilitated program flow control and data management. Its ability to handle interrupts also made it suitable for multitasking applications.

The Intel 8085, introduced in 1976, was an enhancement of the 8080 microprocessor. It maintained a similar architecture but included several key improvements. Notably, the 8085 had a built-in clock oscillator, simplifying system design by eliminating the need for external clock circuitry. It also featured a 5-bit control signal for status line management, which allowed for more flexible interfacing with peripheral devices. The 8085 was capable of running at speeds of up to 3 MHz and had an extended instruction set with 74 instructions.

One of the standout features of the 8085 was its support for 5 extra instructions for stack manipulation and I/O operations, which optimized the programming process. Additionally, it supported serial communication, making it suitable for interfacing with external devices. Its 16-bit address bus retained the 64 KB memory addressing capability of its predecessor.

Both the 8080 and 8085 microprocessors laid the groundwork for more advanced microprocessors in the years that followed. They demonstrated the potential of integrated circuits in computing and influenced the design and architecture of subsequent Intel microprocessors. Their legacy endures in the way they revolutionized computing, making technology accessible to a broader audience, and their influence is still felt in the design and architecture of modern microprocessors today.
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