1. Bridging the Gaps
Electronic Interconnect Protocols
Chintalagiri Shashank
Department of Physics
Indian Institute of Technology, Kanpur
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

2. 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.
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

3. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

4. The Need for Communication
 Any technical system involves
multiple disparate systems.
element 2  In the absence of inter-device
communication, a human being
element 1
would potentially require to
interact with multiple systems.
element 3
 Some elements may not be
amenable to easy Human User
Interface without a major increase
in price and complexity
User
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

5. Inter-device Communication
 Making each of the individual
elements talk to each other element 2
could reduce human
interface requirements to a element 1
single element.
 In many cases, inter-device element 3
communication could reduce
the processing load on the
user. Processing / User Interface element
User
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

6. 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?
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

7. 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.
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

8. Network Configurations
Star Bus
element element
element
element element
element
element
element 1
element
element
element
element
 A real life network is usually a combination of the star and bus
configurations
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

9. Common Communication Protocols
 USART / RS-232
 Parallel Ports
 Serial Peripheral Interface (SPI)
 2-Wire Bus (I2C)
 GPIB (IEEE 488.2)
 Universal Serial Bus (USB)
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

10. Requirements of Communication
 Physical Layer
 Electromagnetic Wave Guides
 Standard Datastream Format
 Synchronization
 Bus Clocks
 Timing
 Checks and Balances
 Negotiation for Communication Line Control
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

11. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

12. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

13. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

14. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

15. 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

16. 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.
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

17. Bus Masters
element 1 element 2 element 3 Bus Master
 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
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

18. More (about) Bus Masters
Inactive Bus Master
element 2 element 3 Active Bus Master
(Slave)
 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.
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in

19. Questions
February 16, 2008
Vyakhya, Techkriti'08 chintal@iitk.ac.in