Communication

Question 1

What do two conductors isolated from each other form

Answer 1

A Capacitor

Question 2

What does the Capacitive Reactance Formula imply about capacitors

Answer 2

That capacitors act as resistors, and at higher frequencys this resistance is higher

For embedded communication, this means that higher frequencies will result in more degradation in the signal

Question 3

If the quantification of information is entropy, how can we measure the information content of a message

Answer 3

We can measure the surprise value of the message

Question 4

Parallel preceded Serial, what can the challenge of this be at high speeds

Answer 4

For parallel to work correctly all signals need to arrive at the same time, this can be challenging at higher speeds

Question 5

What does Baud rate describe

Answer 5

The number of bits per second, i.e. 9600 Baud = 9600 pulses per second

Question 6

How can the Baud rate be recognised automatically

Answer 6

Make the first character always the same. such as 0x55

Question 7

What simple hardware can be used when implementing SPI, what does this mean

Answer 7

A shift register, this makes them cheap

Question 8

To connect one master with 2 slaves for SPI, how many wires are required and what are they (Assume a common ground)

Answer 8

5:
- SCLK - Serial Clock driven by the master
- MOSI - Master Out, Slave In
- MISO - Master In, Slave Out
- CS1 - Chip Select for the first slave (Active Low)
- CS2 - Chip Select for the second slave (Active Low)

Question 9

What does it mean for communication to be Full-Duplex

Answer 9

Full-Duplex means that devices can send and receive signals simultaneously

Question 10

What does it mean for communication to be Half-Duplex

Answer 10

It means devices can either be sending OR receiving, but not both (at one time)

Question 11

I²C uses two wires pulled to high, what do chips need to do to send a signal on this

Answer 11

Pull the line to low with a transistor

Question 12

Where is I²C used

Answer 12

On PCB’s due to the capacitance of the lines

Question 13

What should you use as the pull up resistor if you want fast com’s on an I²C bus

What is the drawback of this

Answer 13

A Low resistance resistor such that the line charges faster,

This will result in higher power usage

Question 14

What should you use as the pull up resistor if you want low power usage on an I²C bus

What is the drawback of this

Answer 14

A high resistance resistor such that less power is lost charging the line

This will result in slower communications

Question 15

Who assigns the addresses of I²C devices, what issue can arise as a result of this

Answer 15

The device manufacturers, this can cause issues as addresses may clash

Question 16

Two masters can be used on one I²C bus, with bus arbitration being used to decide who can talk and who has priority. What is the issue with this for Real-Time Systems

Answer 16

Bus arbitration takes a non-deterministic amount of time if it is not done carefully

Question 17

How many devices can be connected via SPI

Answer 17

One SPI Bus can connect one Master to an unlimited number of devices (limited by the number of chip selects)

Question 18

How many devices can be connected via UART

Answer 18

One UART connection can connect two devices

Question 19

How many devices can be connected via I²C

Answer 19

128 if 7 bit addressing is used, or 1024 if 10 bit addressing is used

Question 20

Is SPI Full-Duplex or Half-Duplex

Answer 20

Full-Duplex

Question 21

Is UART Full-Duplex or Half-Duplex

Answer 21

Full-Duplex

Question 22

Is I²C Full-Duplex or Half-Duplex

Answer 22

Half-Duplex

Question 23

An I²C is 1 Byte what does this contain (by default)

Answer 23

A 7 bit address and 1 bit to signify if the device with that address should read or write