CHAPTER 2

SOSSA FUNCTIONAL DESCRIPTION

2.1WHAT TH E 808SA IS

The 8085A is an 8-bit general-purpose micro- processor that is very cost-effective in small systems because of its extraordinarily low hard- ware overhead requirements. At the same time it is capable of accessing up to 64K bytes of memory and has status lines for controlling large systems.

2.2WHAT'SIN THE 808SA

In the 8085A microprocessor are contained the functions of clock generation, system bus con- trol, and interrupt priority selection, in addition to execution of the instruction set. (See Figure 2-1.) The 8085A transfers data on an 8-bit, bi- directional 3-state bus (ADo-7)which is time- multiplexed so as to also transmit the eight lower-order address bits. An additional eight lines (Aa.15) expand the MCS-85 system memory addressing capability to 16 bits, thereby allow- ing 64K bytes of memory to be accessed direct- ly by the CPU. The 8085A CPU (central process- ing unit) generates control signals that can be used to select appropriate external devices and

INTA RST6.5 TRAP

functions to perform READ and WRITE opera- tions and also to select memory or 1/0 ports. The 8085A can address up to 256 different 1/0 locations. These addresses have the same numerical values (00 through FFH) as the first 256 memory addresses; they are distinguished by means of the 101M output from the CPU. You may also choose to address 1/0 ports as memory locations (Le., memory-map the 1/0, Section 3.2).

2.2.1Registers

The 8085A, like the 8080, is provided with inter- nal 8-bit registers and 16-bit registers. The 8085A has eight addressable 8-bit registers. Six of them can be used either ~s 8-bit registers or as 16-bit register pairs. Register pairs are treated as though they were single, 16-bit registers; the high-order byte of a pair is located in the first register and the low-order byte is located in the second. In addition to the register pairs, the 8085A contains two more 16-bit registers.

 

 

 

 

B

(8)

C

(8)

REG.

 

REG.

 

D

(8)

E

(8)

REG.

 

REG.

 

H

(8)

L

(8)

REG.

 

REG.

 

STACK POINTER

(16)

PROGRAM COUNTER (16)

POWER{-+5V

SUPPLY _GND

.sTIMING AND CONTROL

X,

X2

REGISTER ARRAY

As-,s

ADo•7

ADDRESS BUS

ADDRESSIDATA BUS

FIGURE 2·1 808SA CPU FUNCTIONAL BLOCK DIAGRAM

2-1

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Intel MCS-80/85 manual Whatsin the 808SA, ·1 808SA CPU Functional Block Diagram
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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.
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