Bridging the Gaps : Electronic Interconnect Protocols

February 16, 2008Vyakhya, Techkriti'08 [email protected]

Bridging the GapsElectronic Interconnect Protocols

Chintalagiri ShashankDepartment of Physics

Indian Institute of Technology, Kanpur


Introduction

The technical world depends on various discrete elements, each having its own peculiarities. Each of these elements need to communicate with each other for many reasons, and the subsystems responsible for this communication have to efficiently allow the systems to talk to each other without compromising on the individuality of each of the elements. In the talk, I intend to introduce the basic elements of an arbitrary communication protocol, touching upon the fundamental tasks involved in getting an arbitrary packet of information from one system to another. I will be concentrating on communication between nearby systems in a small number, as opposed to ethernets and TCP/IP.


Agenda

The need for communication.

Common communication protocols

Synchronizing communication - clocks and timing

Serial vs Parallel, why new protocols tend to be serial

Bringing order to the chaos - Bus Masters


The Need for Communication

Any technical system involves multiple disparate systems.

In the absence of inter-device communication, a human being would potentially require to interact with multiple systems.

Some elements may not be amenable to easy Human User Interface without a major increase in price and complexity

element 1

element 2

element 3

User


Inter-device Communication

Making each of the individual elements talk to each other could reduce human interface requirements to a single element.

In many cases, inter-device communication could reduce the processing load on the user.

element 1

element 2

element 3

User

Processing / User Interface element


Is this new?

Traditional instrumentation rarely possess inter-device communication capability.

Instrumentation available today have started to have multiple device interfaces.

Why is the trend going towards extensive inter-device communication?


Why is this new?

Electronic datastreams are much faster than they were in the past.

Cheap and easily accesible high-performance computing helps ease the communication process and enhances the data processing capability within the system.


A real life network is usually a combination of the star and bus configurations

Network Configurations

element 1element

element

element

element

element

element

element

element

element

element

element

Star Bus


Common Communication Protocols

USART / RS-232 Parallel Ports Serial Peripheral Interface (SPI) 2-Wire Bus (I2C) GPIB (IEEE 488.2) Universal Serial Bus (USB)


Requirements of Communication

Physical Layer Electromagnetic Wave Guides

Standard Datastream Format Synchronization

Bus Clocks Timing

Checks and Balances Negotiation for Communication Line Control


Synchronizing Communication

Why synchronize? Packets of data lose meaning if bits are displaced Unsyncronized communication causes significant

data loss, and makes for a very inefficient communication technique.

Clocks vs Timing Clocks need an extra wire, increase the possibility

of errors over physical distances. Timing requires very precise electronics


Checks and Balances

Physical Communication Lines cannot always be trusted : Signal deterioration over the length of the

waveguide Momentary desynchronization of the datastream Electromagnetic Interference from external EM

sources Hardware failures Inappropriate datastreams from bad elements on

the bus


Checks and Balances

Data Verification Procedures Parity checks Data Recieved Acknowledgement Hashes and Sums

Data Integrity Issues are more pronounced with High Speed Data Transfer Transmission over longer distances Large number of communicating devices on the bus


Serial vs Parallel

These two represent diametrically opposite paradigms in the way communication is done

Serial communication send bits one a time on a single wire.

Parallel communication sends all the bits in one shot. Absolutely parallel communication is usually not

practically feasible


Serial vs Parallel

Newer generic communication protocols are predominantly serial in nature Serial communication sends less information per

clock Serial communication can run at greater clocks

beacuse each bit can be sent faster Waiting for multiple lines to settle, especially at high

speeds, is the key. Serial communcation also has narrower cables.

Smaller number of data lines makes for less EM Interference


A Cacophony of Data

element 1 element 2 element 3

If every device starts talking at the same time, noise ensues.

There needs to be a mechanism to maintain a semblance of order.


Bus Masters

element 1 element 2 element 3

A single device on the bus is given a special privilege – control of the communication lines.

The Bus Master decides who talks when, and in some cases also orders a particular device to listen.

The Bus Master is usually a computer or a microcontroller – an 'intelligent' device.

In general, the Bus Master generates the clock

Bus Master


More (about) Bus Masters

When you need more than one device to have control, your communication protocol becomes more complex.

Procedures for control negotiation between the Masters are built into some procedures.

These are called Multi-Master Busses.

Inactive Bus Master(Slave)

element 2 element 3 Active Bus Master


Questions