inter 8080Al8080A·1/8080A·2

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 8 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.

Double precision operators such as stack manipulation and double add instructions extend both the arithmetic and interrupt handling capability of the 8080A. 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 ability to rotate the accumulator I~ft or right through or around 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 DAA instructions provide decimal arithmetic capability. 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 8080A is stored in the form of 8-bit binary integers. All data transfers to the system data bus will be in the same format.

I D7 D6 D5 D4 D3 D2 D1 Dol

DATA WORD

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

 

 

 

 

 

 

 

 

 

 

ID7 D6 D5 D4

D3

D2

DtYDJ OP CODE

Register to register, memory refer-

ence, arithmetic or logical, rotate,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

return, push, pop, enable or disable

 

 

 

 

 

 

 

 

 

Interrupt instructions

 

Two Byte Instructions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ID7 D6 D5 D4

D3

D2

D1

Do I OP CODE

 

ID7 D6 D5 D4

D3

D2

D1

Do I OPERAND

Immediate mode or I/O instructions

 

Three Byte Instructions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I D7 D6 D5 D4

D3

D2

D1

Do I OP CODE

Jump, call or direct load and store

ID7 D6 D5 D4 D3 D2

D1

Do I LOWADDRESSOR OPERAND 1

instructions

 

ID7 D6 D5 D4 D3 D2

D1

Do I HIGH ADDRESSOR OPERAND 2

 

 

 

 

 

 

 

 

 

 

 

For the 8080A a logic "1" is defined as a high level and a logic "0" is defined as a low level.

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Intel MCS-80/85 manual Data and Instruction Formats

MCS-80/85 specifications

The Intel MCS-80/85 family, introduced in the late 1970s, is a seminal collection of microprocessors that played a pivotal role in the early days of computing. The MCS-80 series, initially targeting embedded systems and control applications, gained remarkable attention due to its innovative architecture and flexible programming capabilities.

The MCS-80 family is anchored by the 8080 microprocessor, which was one of the first fully integrated 8-bit microprocessors. Released in 1974, the 8080 operated at clock speeds ranging from 2 MHz to 3 MHz and featured a 16-bit address bus capable of addressing up to 64KB of memory. The processor’s instruction set included around 78 instructions, providing extensive capabilities for data manipulation, logic operations, and branching.

Complementing the 8080 was a suite of support chips, forming the MCS-80 platform. The most notable among them was the 8155, which integrated a static RAM, I/O ports, and a timer, tailored for ease of designing systems around the 8080. Other support chips included the 8085, which provided improvements with an integrated clock generator, making it compatible with more modern designs and applications.

The MCS-85 series, on the other hand, revolves around the 8085 microprocessor, which provided a more advanced architecture. The 8085 operated at clock speeds of up to 6 MHz and came with a 16-bit address bus, similar to its predecessor. However, it introduced more sophisticated features, including an enhanced instruction set and support for interrupt-driven programming. These enhancements made the 8085 especially appealing to developers working in real-time processing environments.

The MCS-80/85 family utilized NMOS technology, known for its lower power consumption and higher performance compared to previous technologies like TTL. The family’s architecture allowed for easy interfacing with a variety of peripherals, making it a favorite for educational institutions and hobbyists embarking on computer engineering projects.

With its robustness, versatility, and affordability, the Intel MCS-80/85 microprocessors laid the groundwork for many subsequent microcomputer systems and applications. The legacy of this powerful family continues to influence modern microprocessor design, emphasizing the importance of reliable architecture in a rapidly evolving technology landscape.