GPIO

Question 1

What are I/O registers?

Answer 1

addresses associated with I/O devices

Question 2

What is a driver?

Answer 2

Software that communicates with an I/O device. Other programs call functions in the device driver to access the device without having to understand lower-level hardware

Question 3

What is an embedded I/O system?

Answer 3

a programmed controller (comp./microcont.) with a dedicated function within a larger mechanical/electrical system, often with real-time computing constraints

Question 4

What does an embedded I/O system usually include?

Answer 4

• input device (peripheral)
• controller (computer/microcontroller)
• output device (peripheral)

Question 5

MCU - GPIO

Answer 5

• used to write/read digital signals
• requires registers to read input, pin values, write output in values and set directions of the pin
• requires configuration registers (interrupts, pin type, rising falling edge)

Question 6

What is the purpose of an I/O interface?

Answer 6

To manage communication between peripherals and the computer. It resolves differences between the peripherals and CPU

Question 7

What are the four major differences between peripherals and computers?

Answer 7

1) data format in peripherals, word format in CPU and memory
2) operating modes of peripherals differ, must be controlled
3) peripherals are often electromechanical devices which operate differently from CPU and memory (electronic devices), therefore conversion signals may be required
4) data-transfer rate of peripherals and clock rate of CPU, synchronisation required

Question 8

What are interface units?

Answer 8

• special hardware components between the CPU and peripherals which supervise/synchronise all input and output transfers
• interface between CPU bus and peripherals

Question 9

What is the purpose of the clock?

Answer 9

• synchronises all data transfer

- generates signal for timers, PWM and other peripherals

Question 10

Give two clock sources

Answer 10

• mechanical resonant devices such as crystals or ceramic resonators
• RC oscillators

Question 11

What is the purpose of prescaling?

Answer 11

• used to divide the clock seed the timer as it is too high for counter register (16 bit) to hold

Question 12

What is the Auto Reload Reigster (ARR)

Answer 12

• further divide system clock to give timer frequency

- counter counts up to value in ARR before reloading

Question 13

pulse width

Answer 13

“on time”

Question 14

duty cycle

Answer 14

pulse width divided by period

Question 15

What is the Capture Compare Register (CRR)?

Answer 15

• compared to counter and raises a signal when equal
• one CRR for each channel
• used to change pulse with

Question 16

What happens when an external interrupt is raised?

Answer 16

The MCU stops its current task, branches to an ISR which gets executed, then returns to previous task

Question 17

What are the different standards for Serial I/O

Answer 17

• SPI
• UART (RS 232/485)
• I2C

Question 18

Describe SPI

Answer 18

Interface requires three lines minimum:

• SCK
• MOSI
• MISO
• CE/CS which can be used to select a peripheral

Question 19

Describe an SPI transmission:

Answer 19

• master (MCU) produces clock signal
• master initiates communication with series of clock pulses
• master puts data on MOSI starting with m.s.b (sending)
• slave puts data on MISO (receiving)

Question 20

Describe UART

Answer 20

• communication without a clock, therefore devices aren’t synchronised (asynchronous)
• system agrees on data rate, each device generates its own clock
• slower than SPI
• protocols include RS-232 and RS-485

Question 21

What is the purpose of the parity bit in RS-232 protocol for UART? How does it work?

Answer 21

• used to detect data corruption
• configured as even or odd
• for even parity, parity bit is chosen so total collection of data (incl. parity bit) has an even number of 1’s
• receiver checks if even number of 1’s was received and signals an error if not
• odd parity is reverse

Question 22

What is Baudrate (RS-232 protocol)?

Answer 22

• signalling rate measured in symbols/sec
• multi-level signalling (multiple bits per symbol)
• 2-level signalling (each symbol represents a bit)

Question 23

RS-485 protocol for UART

Answer 23

• does not define a protocol, defines an electrical interface
• uses differential signalling to enable data transmission over long distances
• noise rejection

Question 24

Describe I2C

Answer 24

interface requires two lines, one for bidirectional data signals (SDA), one for the clock signal (SCK). Bus drivers are open drain, can pull signal line low but not drive it high, so each signal line requires a pull-up resistor

Question 25

Explain how an I2C transmission occurs

Answer 25

START CONDITION:
- master leaves SCL high
- pulls SDA line low
- generates clock pulses
ADDRESS FRAME:
- always sent first for new communication
- 7 bit address (m.s.b first)
- R(1) or W(0) bit indication
DATA FRAME:
- sent based on R/W
- length is arbitrary
STOP CONDITION:
- SCL pulled high
- SDA pulled high

Question 26

High speed serial:

Answer 26

• encoded data containing both data and clocking info sent in a single differential signal
• speeds up to 10 Gbps