SPI and I2C

Question 1

What are I2C and SPI

Answer 1

I2C and SPI are fast, synchronous comunication protocol that though relatively complex enable multiple devices to be connected

Question 2

compare UART to I2C and SPI

Answer 2

▪ UART is slow
▪ UART allows only a limited number of devices
▪ UART is simple
▪ UART is asynchronous

Question 3

what architecture does the I2C work on

Answer 3

Operates on a controller-target architecture
Two lines are:
* Serial Data (SDA): Line for controller and target to send and receive data
* Serial Clock (SCL): Clock signal line

Question 4

advantages of I2C

Answer 4

Advantages:
▪ Allows multiple controllers and target peripherals
▪ Clock stretching
▪ 7 to 10 bit addressing (127+ devices)
▪ Two wires
▪ Synchronous
▪ Low power consumption
▪ Faster than serial ports (9600 baud = 9.6 kpbs)
▪ Data transmission acknowledgement
▪ Arbitration
▪ Variable data rates
▪ Acknowledgement/error detection

Question 5

Disadvantages of I2C

Answer 5

Disadvantages:
▪ Half duplex
▪ Data overhead (12+ bits sent for every 8 bits of data)
▪ Speed not as fast as SPI (5 Mbps with Ultra Fast Mode)

Question 6

Start condition for I2C

Answer 6

Controller sets SCL high (1) and pulls SDA low (0), which informs all peripherals that transmission is to start

Question 7

Address Frame for I2C

Answer 7

Controller indicates which target peripheral is being sent data. MSB of 7 bit address sent first (27 (128)
possible addresses)

Question 8

what is the ACK/NACK bit

Answer 8

Every 9th bit, target peripheral given control. If SDA does not go low (0) before 9th clock pulse we can infer that
transmission failed

Question 9

what are the stop conditions for I2C

Answer 9

Defined by Low to High transition on SDA AFTER a low to high transition on SCL, with SCL staying high
afterwards. SDA should not change between SCL rising and subsequently falling, risk of false stop

Question 10

I2C writing

Answer 10

When the controller writes to the target peripherals the information sent by the controller is in blue in above diagram,
information sent by the peripheral is orange. R/W control bit is 0

Question 11

I2C reading

Answer 11

When the controller reads from the target peripherals the information sent by the controller is in blue in above
diagram, information sent by the peripheral is orange. R/W control bit is 1

Question 12

what is the SPI

Answer 12

SPI is a 4 wire, full duplex synchronous serial communication mode which
uses a controller-target architecture

Question 13

what is the architecture of SPI

Answer 13

A controller-target architecture means the controller is the controlling
device, with other devices called targets taking instruction from the
controller, in theory, you can have infinite targets but in reality, this is
limited by loading issues

Question 14

what does SPI stand for

Answer 14

Serial Peripheral Interface

Question 15

what does the controller do in SPI

Answer 15

• The Controller can initiate data transmission at any time by outputting
  clock signal (SCLK) to synchronise Target
• Only the Controller can generate clock signal
• The Target is synchronised on the falling or rising clock edge
  Controller reads bits as received
  The Controller can select clock polarity and
  phase

Question 16

Advantages of SPI

Answer 16

Advantages
▪ No start and stop bits – continuous stream of data, no overhead
▪ High data transmission rates (10 Mbps)
▪ Full duplex

Question 17

Disadvantages of SPI

Answer 17

Disadvantages
▪ Four wires
▪ No error checking
▪ No data transmission acknowledgement
▪ Single Controller