Software Compatibility

INTRODUCTION TO MCS-85™

As with any computer system the cost of soft- ware development far outweighs that of hard- ware. A microcomputer-based system is tradi- tionally a very cost-sensitive application and the development of software is one of the key areas where success or failure of the cost ob- jectives is vital.

8080A		808SA
PROGRAMS		SYSTEM
PROGRAMS		SYSTEM

The 8085A CPU is 100% software compatible with the Intel® 8080A CPU. The compatibility is at the object or "machine code" level so that ex- isting programs written for 8080A execution will run on the 8085A as is. The value of this becomes even more evident to the user who has mask programmed ROMs and wishes to update his system without the need for new masks.

PROGRAMMER TRAINING

A cost which is often forgotten is that of pro- grammer training. A new, or modified instruc- tion set, would require programmers to relearn another set of mnemonics and greatly affect the productivity during development. The 100% compatibility of the 8085A CPU assures that no re-training effort will be required.

BOBOA		8080A
DEVELOPMENT		PROGRAM
TOOLS		LIBRARIES

MCS_85™

For the new microcomputer user, the software compatibility between the 8085A and the 8080A means that all of the software development tools that are available for the 8080A and all software libraries for 8080A will operate with the new design and thus save immeasurable cost in development and debug.

The 8085A CPU does however add two instruc- tions to initialize and maintain hardware features of the 8085A. Two of the unused op- codes of the 8080A instruction set were designated for the addition so that 100% com- patibility could be maintained.

HARDWARE COMPATIBILITY

The integration of auxiliary 8080A functions, such as clock generation, system control and interrupt prioritization, dramatically reduces the amount of components necessary for most systems. In addition, the MCS-85 operates off a single + 5 Volt power supply to further simplify hardware development and debug. A close ex- amination of the AC/DC specifications of the MCS-85 systems components shows that each is specified to supply a minimum of 400ltA of source current and a full TTL load of sink cur- rent so that a very substantial system can be constructed without the need for extra TTL buf- fers or drivers. Input and output voltage levels are also specified so that a minimum of 350mV noise margin is provided for reliable, high- performance operation.

PC BOARD CONSIDERATIONS

The 8085A CPU and the 8080A are not pin- compatible due to the reduction in power sup- plies and the addition of integrated auxiliary features. However, the pinouts of the MCS-85 system components were carefully assigned to minimize PC board area and thus yield a smooth, efficient layout. For new designs this incompatibility of pinouts presents no pro- blems and for upgrades of existing designs the reduction of components and board area will far offset the incompatibility.

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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.

Intel MCS-80/85 manual Software Compatibility

Models: MCS-80/85

INTRODUCTION TO MCS-85™