Digital communication protocols (week 6) Flashcards
What types of devices share information amongst themselves ?
-multiple controller system
-master slave setups
-microcontroller with external sensors
Why do we need communication protocols ?
Because usually several digital devices need to share information amongst themselves.
How do communication protocol propose to implement communication ?
On an external bus.
They are different architectures for a given system. What are they ?
- centralised architecture
-hierarchical architecture
-distributed architecture
What is centralised architecture ? What are the pros and cons
use of one central computer to control entire plant.
Pros: easy to implement, inexpensive (single control unit)
cons: interdependency, if the central fails, all control is lost. Old day to do things, as now most Systems are multi-computer based.
What is the hierarchical architecture? Pros and cons ?
It is a hierarchy of computers.
The labour is divided between the commuters according to the function involved.
There is a specialisation of computers.
There are units handling routine tasks, supervised by units with greater authority.
Pros: Allowing specialisation of tasks allocated. More flexible than centralised. Easy to replace sub-part of the overall system.
Cons: Interdependency is still high. Relies on top level which can be a problem if it doesn’t function well.
What is the distributed architecture? Pros and cons ?
All the devices perform similar tasks and coordinate with each other.
Pros: Specialisation (less than hierarchical). Much more flexible. Can exploit parallelisms & redundancy to improve reliability. In case of failure, work can be transmitted from one computer to another.
Cons: hard to design.
DATA TRANSFER - second decision after deciding the architecture. What are the two main families?
1) parallel communication
2) serial communication
What is parallel communication ? PROS AND CONS
all the bits transferred SIMULTANEOUSLY
Pros: achieve high data transfer rates
Cons: one physical where required for EACH bit, wiring is complex
application: used on very short distances (SMALL WIRES FOR HIGH DATA RATE)
EXAMPLE: GPIB
What is Serial communication ? PROS AND CONS
Data transferred bit by bit in sequence.
Pros: only two wires for DATA and the CLOCK. Easy wiring. Cheaper method
Available in Arduino
Cons: lower data transfer rate.
APPLICATION: used to interface multiple multiple microcontrollers (e.g. CAN bus in automotive), or to communicate with external devices (e.g. SPI and I2C for sensors )
What are serial and parallel communications based on ?
PROTOCOLS (SET OF RULES), such as syntax, semantic, timing
DATA TRANSFER-PARALLEL COMMUNICATION-WHAT IS GPIB?
Used in instruments controlling. It is the General Purpose Instrument Bus (GPIB). It is a very common bus
APPLICATION: Used to communicate with instruments such as oscilloscopes, multimeters.
What are the families of devices of GPIB
Talker (write data to bus)
listener (accept data from bus)
controller (control flow)
What is the protocol of GPIB
- up to 15 devices connected to bus (with different adresses)
- uses negative logic (i.e. 1 corresponds to V<0.8v and 0 corresponds to V>2v.
- data lines can transmit 8-bit data in parallel
-Handshake used to control flow (ATN=0/1, NFRD=0, NDAC=0, DAV=1)
DATA TRANSFER-SERIAL COMMUNICATION- what is I2C?
Serial bus designed for communication between integrated circuits.
families
master clock
slave
