SILICON GATE MOS 8255

Output Control Signal Definition

OBF (Output Buffer Full F/F)

MODE 1 (PORT A)

 

 

The OBF output will go ~'Iow" to indicate that the CPU has

 

 

written data out to the specified port. The OBF F/F will be

CONTROL WORD

 

 

 

set by the rising edge of the WR input and reset by the fail-

 

 

ing edge of the ACK input signal.

r- -

-,

 

I INTE

I

 

I A

I

ACK (Acknowledge Input)

__ .J

 

 

A "Iow" on this input informs the 8255 that the data from Port A or Port B has been accepted. In essence, a response from the peripheral device ind icating that it has received the data output by the CPU.

INTR (Interrupt Request)

A "high" on this output can be used to interrupt the CPU when an output device has accepted data transmitted by the CPU. INTR is set by the rising edge of ACK if OBF is a "one" and INTE is a "one". It is reset by the falling edge ofWR.

INTEA

Controlled by bit set/reset of PC 6.

INTE B

Controlled by bit set/reset of PC 2.

MODE 1 (PORT B)

P~.PBo 8

CONTROL WORD

0 7 0 6 Os 0 4 0 3 O2 0, Do

PC,OBFB

Mode 1 Output

(OUTPUT BUFFER FULL)

/

NO PROTECTION

 

FOR THIS OPERATION

DATA BUS

 

OUTPUT

\

 

 

~- -- - ----- - - ------

Basic Timing Output

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Intel 8080 manual Output Control Signal Definition, Intea

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.