Preliminary Functional Description, System Interface

SILICON GATE MOS 8253

8253 PRELIMINARY FUNCTIONAL DESCRIPTION

In Microcomputer-based systems the most common inter- face is to a mechanical device such as a printer head or step- per motor. All such devices have inherent delays that must be accounted for if accurate and reliable performance is to be achieved. The systems software allows for such delays by programmed timing loops. This type of programming re- quires significant ov~rhead and maintenance of multiple loops gets extremely complicated.

The 8253 Programmable Interval Timer is a single chip so- lution to system timing problems. In essence, it is a group of three 16-bit counters that are independent in nature but driven commonly as I/O peripheral ports. Instead of setting up timing loops in the system software, the programmer configures the 8253 to match his requirements. The pro- grammer initializes one of the three counters of the 8253 with the quantity and mode desired then, upon command, the 8253 will count out the delay and interrupt the micro- computer when it has finished its task. It is easy to see that the software overhead is minimal and that multiple delays can be easily maintained by assigned interrupt levels to dif- ferent counters. Other functions that are non-delay in nature and require counters can also be implemented with the 8253.

•Programmable Baud Rate Generator

•Event Counter

•Binary Rate Multiplier

•Real Time Clock

System Interface

The 8253 is a component of the MC5-80 system and inter- faces in the same manner as all other peripherals of the family. It is treated by the systems software as an array of I/O ports; three are counters and the fourth is a control register for programming. The OUT lines of each counter would normally be tied to the interrupt request inputs of the 8259.

The 8253 represents a significant improvement for solving one of the most common problems in system design and reducing software overhead.

CLKO

DATA

BUSGATE 0

BUFFER

AD --___.a

WR ----- +C11		ClK 1
WR ----- +C11	READ/
	READ/
	WRITE	GATE 1
	lOGIC
		OUT 1

cs------- '

CLK2

	COUNTER	GATE 2
	#2	GATE 2
	#2
		OUT2

INTERNAL BUS

8253 Block Diagram.

ADDRESS BUS (16)

A1 An	0 0 .07
	8253

COUNTERCOUNTERCOUNTER

012

III

lOUT GATE ClK I lOUT GATE ClK I lOUT GATE ClK I

8253 System Interface.

5..170

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.

Intel 8080 manual Preliminary Functional Description, System Interface, Block Diagram

Models: 8080