Connection standards Flashcards
RS-232:
Synchronous or Asynchronous?
Asynchronous transmission
RS-232:
Full duplex or Half duplex or Simplex?
Full duplex
RS-232:
How do the clock signals operate?
Each device has an independent clock
RS-232:
What are the baud rates?
> 14.4 kbits/s
28.8 kbits/s
56 kbits/s
RS-232:
What defines the speed it operates at?
Speeds are greater when the connection distance is shorter
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
RS-232:
What are the voltage levels?
+15V > Logic - 0 > +5V
-15V < Logic - 1 < -5V
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
RS-232:
What are the data lines?
Tx - Transmission
Rx - Recieving
I2C:
Synchronous or Asynchronous?
Synchronous
I2C:
Full duplex or Half duplex or Simplex?
Half-duplex
I2C:
What are the data lines?
> SCL = Clock
SDA = Data line
GND = Ground
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
I2C:
How many devices can be connected to the bus?
More than 2
I2C:
What is the device higherarchy?
> One master device
> Multiple slave devices
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.
