SYSTEM OPERATION

the Intel 2104A and 2117. The 8202 provides the necessary refreshing for such dynamic RAMs, and also provides the control signals required for accessing, selecting, and address clocking. It allows for the use of the 8085A'sfull capabili- ty of 64k bytes of address space with no addi- tional buffering devices. As with other standard memory interfaces, it is necessary to demulti- plex the lower 8 bits of address from the multi- plexed 8085A bus, ADo-7

3.8MINIMUM MCS-85™ SYSTEM

The Schematics of Figure 3.6 depict a minimum system core. In actual use, some of the pro- cessor control signals (TRAP, INTR, and HOLD) would have to be terminated. Also, interface logic to external devices as well as more memory and 1/0 devices may be desirable. The first thing one notices about the system in Figure 3.6 is the scarcity of parts required to build this system. With a minimum of parts, we

have constructed a microcomputer system that has the following functions:

PARTS

FUNCTIONS

1 8085A

1 CPU (Clock cycle

1 8355/8755A

:s 320 ns)

1 8156

2048 Bytes of either

1 Crystal

EPROM or ROM

256 Bytes of RAM

4 Resistors

38110 Lines

1 Capacitor

5 Interrupts

1 Diode

1 Programmable Timerl

1 + 5 Power Supply

 

Counter

 

1 Crystal and Oscillator

 

1 Clock

 

1 Power-on Reset

By looking at the printed circuit layout of Figure 3.7, we can see that not only are there just 3 ICs, but that the interconnection of these p-arts is extremely easy and provides a very dense layout. Expecially notice the easy flow of the system bus on the solder side of the board.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2 X 2142

 

----------_~---ICS2

 

 

 

 

 

 

 

, . ------ t ------- QCSI

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2 X 2142

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CS2

 

 

 

 

 

 

 

, .. ------- <l CSI

 

 

WR

---------

~~-----~~

 

 

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OD

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

/

 

 

 

8205

 

 

 

 

 

 

 

 

 

 

 

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A13

 

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0,

 

 

 

 

 

 

 

 

 

 

 

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A g ,9=0

 

/

All

 

Ao

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2316E

Vee

 

E,

 

 

 

 

 

 

t -

+ ------ <lCSl

 

 

 

 

 

 

 

 

 

 

 

 

 

A,s

 

E,

 

 

 

 

 

 

t ------ <lCS2

 

 

 

 

 

 

 

 

 

 

 

 

 

101M

 

E,

0 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8212

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ao·A?

 

 

 

 

 

 

 

 

=7

AD o ·AD7

01 1 _8

00 1.8

 

 

 

 

 

 

 

 

 

 

 

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/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Vee

 

MD

 

 

 

 

 

 

 

 

 

 

 

 

/

 

 

 

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

STB

 

 

 

 

 

 

 

 

 

 

 

 

I

ALE

 

DS,

=0

 

/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

/11

 

MEMORY ADDRESS

 

 

 

0

1 1 1 I 1 X A. I-

- I-

Ao I

I

 

 

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DS 1

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FIGURE 3·5STANDARD MEMORIES WITH LATCHED ADDRESS AND DECODED CHIP SELECTS

3-7

Page 56
Image 56
Intel MCS-80/85 manual Minimum MCS-85 System, Parts Functions

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.