Connection standards Flashcards by Henry Triff

RS-232:

Synchronous or Asynchronous?

Asynchronous transmission

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RS-232:

Full duplex or Half duplex or Simplex?

Full duplex

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RS-232:

How do the clock signals operate?

Each device has an independent clock

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RS-232:

What are the baud rates?

> 14.4 kbits/s
28.8 kbits/s
56 kbits/s

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RS-232:

What defines the speed it operates at?

Speeds are greater when the connection distance is shorter

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RS-232:

What is the data transfer protocol?

> Data is sent in 8-bit frames (packets)
To start a transmission a 1 bit is sent
A stop 0 bit is sent at the end of each byte followed by a pause

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RS-232:

What are the voltage levels?

+15V > Logic - 0 > +5V

-15V < Logic - 1 < -5V

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What is the difference between RS-232 and UART?

> They are the same but a lot of the RS-232 standards are ignored for UART
Voltage levels are flexible
Longer frames/packets are allowed
Can connect to USBs

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RS-232:

What are the data lines?

Tx - Transmission

Rx - Recieving

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I2C:

Synchronous or Asynchronous?

Synchronous

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I2C:

Full duplex or Half duplex or Simplex?

Half-duplex

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I2C:

What are the data lines?

> SCL = Clock
SDA = Data line
GND = Ground

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I2C:

What type of outputs Circuits are used? How does this work?

> Open-collector bus digital outputs.

> Any device can pull the data line low

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I2C:

How many devices can be connected to the bus?

More than 2

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I2C:

What is the device higherarchy?

> One master device

> Multiple slave devices

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I2C:

What are the transmission speeds?

> Standard mode: 100 kbits/s
Fast mode: 400 kbits/s
Fast mode+: 1 Mbits/s
High speed mode: 3.4 Mbits/s

I2C:

What is the transmission sequence?

During an idle period, a device that wished to take control can initiate the process the pulling the data line low.
All devices wait for the data that follows which consists of a 7-bit address and a direction bit.
> The direction identifies if the device should transmit data or wait and listen for more data.
> If two devices attempt to initiate communication at the same time and arbitration process commences

I2C:

How does addressing work?

> Address identifies the intended slave device.
This is predetermined by device manufacturers
Duplication of device addresses is done using a central register of IC addresses
ICs often allow the address to be varied

I2C:

How does clock signals work?

> New data is only transmitted on the rising edge of the clock signal (SCL)
If a device is struggling to keep up with the incoming data it can slow down the transfer by holding the clock line low momentarily to prevent the transmitting device from moving on to the next bit.

I2C:

What are the rise times for different transmission speeds?

> Standard mode: < 1μs
Fast Mode: < 300ns
Fast + Mode: < 120ns

SPI:

Full duplex or Half duplex or Simplex?

Full-duplex transmission

SPI:

What type of outputs Circuits are used?

Tri-state push-pull digital outputs

SPI:

What is the maximum speed transfer?

100Mbits/s

SPI:

What are the bus lines?

> SCLK = Serial Clock
MOSI = Master Out Slave In
MISO = Master In Slave Out
SS/CS = Slave Select / Chip Select

SPI: | What is the purpose of SS/CS?

Tells the individual slave devices to respond to incoming data

SPI: | Synchronous or Asynchronous?

Synchronous transfer

SPI: | What is the clock timing?

Data is traveling on the rising edge of the clock line, but this can be changed depending on the SPI mode

SPI: | How many CS/SS are needed?

One for every slave device

SPI: | What is the arbitration process?

MOSI/MISO is uni-directional so no bus arbitration procedure required

CAN-Bus: | What does CAN stand for?

Controller Area Network (CAN) bus system

CAN-Bus: | What type of outputs Circuits are used?

Open-collector

CAN-Bus: | What are the conductors?

CAN-High (CANH) CAN-Low (CANL) > Shielded twisted-pair wires. This is because it provides noise immunity which is essential for electrically harsh enviroments > Common-mode noise will be rejected > Must be terminated at both ends by a resistor equal to the impedance of each cable

CAN-Bus: | What are the voltage levels?

> HIGH = Both CANH and CANL are 2.5V | > LOW = CANH is 3.5V, CANL is 1.5V

CAN-Bus: | How far can it operate at?

Long distances

CAN-Bus: | What is the communication protocol?

``` > Every device is a master > All devices can talk at the same time > There is an arbitration process > Data is not addressed, all devices listen and can do something with the data > There is an agreed data format ```

CAN-Bus: | What is the arbitration process?

> It prioritises masters according to their address > Most important masters have an address with several 0s > Essentially the important masters win the right to use the bus

CAN-Bus: | What are the data speeds?

> Short distances = 1 Mbits/s | > Long distances = 10 kbits/s

CAN-Bus: | Synchronous or Asynchronous?

Asynchronous

CAN-Bus: | How do clocks work?

> Every device has the same bit rate (baud rate) > Each time a logic HIGH is asserted the receivers re-synchronise their clocks. > No more than 5 consecutive bits can be the same polarity HIGH or LOW to ensure the receiver clocks stay in synchronisation.