SILICON GATE MOS 8257

8257 PRELIMINARY FUNCTIONAL DESCRIPTION

The transfer of data between a mass storage device such as a floppy disk or mag cassette and system RAM memory is often limited by the speed of the microprocessor. Removing the processor during such a transfer and letting an auxiliary device manage the transfer in a more efficient manner would greatly improve the speed and make mass storage devices more attractive, even to the small system designer.

The transfer technique is called DMA (Direct Memory Ac- cess); in essence the CPU is idled so that it no longer has control of the system bus and a DMA controller takes over to manage the transfer.

The 8257 Programmable DMA Controller is a single chip, four channel device that can efficiently manage DMA activ- ities. Each channel is assigned a priority level so that if multi-DMA activities are required each mass storage device can be serviced, based on its importance in the system. In

operation, a request is made from a peri phera I device for access to the system bus. After its pr iority is accepted a HOLD command is ussued to the CPU, the CPU issues

aHLDA and that DMA channel has complete control of the system bus. Transfers can be made in blocks, suspending the processors operation during the entire transfer or, the transfer can be made a few bytes at a time, hidden in the execution states of each instruction cycle, (cycle-stealing).

The modes and priority resolving are maintained by the system software as well as initializing each channel as to the starting address and length of transfer.

The system interface is si mi lar to the other peri phera Is of the MCS-80 but an additional 8212 is necessary to control the entire address bus. A special control signal BUSEN is connected directly to the 8228 so that the data bus and control bus will be released at the proper time.

\

~

~

1/ V

As-A,5

8

ADDRESS BUS (16)\

CONTROL BUS

 

\

 

 

flOW

ilOR

HOLD

RESET

DATA BUS (8)

 

\

4:/'\~

MEMR

MEMW

READY

 

/ A o-A3 /A4 -A7

' ---

8212

BUSENt t

8228I 1

l/L-- 8

['r -

HLDA 92(TTL)

"',/7

CS A ·A

A

4

-A

 

AOSTB AEN

0

7

-0

0

I/O

MEM

HOLD HLOA

CLK

ROYIN

RESET

o 3

 

7

 

 

 

 

 

if W

 

 

 

 

 

 

 

 

 

 

 

 

 

 

W R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8257

 

 

 

 

 

 

 

 

 

128/256

 

 

 

 

 

DACK

ORO

DACK

ORO

DACK

ORO

DACK

ORO

 

 

 

MOD

TC

 

 

 

 

3

3

2

2

1

1

0

0

 

 

 

~

!

 

 

 

 

~

t

l

t

l

1

l

f

I

OMA CHANNEL REOUESTS AND ACKNOWLEDGES

System Interface 8257.

ADDRESS BUS

 

ORO 0 ...... ----- 11

 

SYSTEM

 

DACK 0 1------..

DISK 1

 

RAM

 

ORO 11 .. ----- 1

 

MEMORY

8257

DACK 1 I ___ ----- . t

 

 

AND

 

 

ORO 2 ......---- 11

 

 

8212

 

 

 

DACK 2 1------...

DISK 2

 

 

ORO 3 1+ ------ 1

 

 

 

 

 

DACK 31--------..

 

 

OMA CONTROLLER

DUAL FLOPPY DISK CONTROLLER

 

System Application of 8257.

5-172

Page 243 Page 245
Page 244
Image 244
Intel 8080 manual System Interface, Dack 2, System Application
Page 243 Page 245

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.
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