Networking and communications

Theory / lecture notes

Networking purposes:

location
parallelism
modularity
interference

UART

no clock, but fixed speed

NB. TX connects to RX (and vice versa).

I2C

I2C is aka TWI

7-bit addresses (mostly)

Uses these pins:

SCL = clock
SDA = data

Open-Drain Logic: I²C uses open-drain drivers, meaning devices can only pull the lines (SDA and SCL) down to ground (low state); they cannot drive them high directly. Instead:

High State: Pull-up resistors connected to the supply voltage ensure the lines return to a high state when no device is pulling them low.

Low State: Devices actively pull the lines down to ground.

This design allows multiple devices to share the same bus without conflicts, but it relies on pull-up resistors for proper operation.

Most boards that speak a certain protocol have built in pullup/down resistors.

SPI

Has clock and data lines
data out / data in (sdo/sdi)(MOSI/MISO)(PICO/POCI)
More pins than I2C

Advantage: more pins = higher data rate

SCLK - clock
SS/CS - Chip select / enable
MOSI (Master Out secondary In): This pin carries data from the master device to the secondary device. It is used for sending commands or data.
MISO (Master In secondary Out): This pin carries data from the slave device back to the master device, typically used for receiving responses.

CPOL (Clock Polarity) parameter determines the idle state of the clock signal when no data is being transferred.

serial bus daisy chain

(Star) 1 main with many secondaries topology UART / SPI

Ring topology neopixels / SPI

Bus topology main with one big data line and main/secondaries connected to it needs a network address (MAC address, for eg.)

TCP/IP

protocol used on the internet

OSI layers (7 layers) - standardizes how networks interact / communicate

physical
ethernet - Handles communication between devices on the same local network using MAC addresses.
network layer - IPV4/6 - routing data packets between different networks, ensuring that data reaches its intended destination.
transport layer TCP (data) / UDP (streaming - faster - throws data like a potato) - with TCP/IP you always get back an acknowledge
session layer - how we're talking - HTTP - peer to peer
presentation - encryption
application - Defines how users interact with the network through applications.
Every device on a network has a unique IP address, which identifies it for communication.
Networks are divided into subnets, each with a default gateway (the router that connects the subnet to other networks).

DHCP is a protocol that automatically assigns IP addresses and other settings to devices on a network.

Wireshark is a program that lets us see which packages out computer is sending and receiving, that would otherwise go unnoticed.

wireshark

Group project

Connect two devices
Show logic analyzer between them
Do so using I2C and SPI

I2C communication

ESP32 Arduino I2C tutorial

I2C tutorial

The secondary must write it's own I2C address (this is done in the code).

AND

Set callback functions:

to read received messages
to handle requests

Irja and Sam uploaded the code to their ESP32s and used cables to connect to one another.

NB. Power the master ON first.

arduino reading

request received

To get a better understanding of how the MCUs are communicating, we hooked certain pins (always Ground first) up to the Logic analyzer and used the program, Logic, to view the signals.

Channel 12 clock Channel 5 SDA

NB. When opening Logic specify which protocol is being used (I2C).

Remember the screenshot of Erwin's slides about the transmissions sequence of an I2C signal?

This is that! (W0x55-0x48-0x65-0x6C•0x6C-0x6F-0x20-0x57-0x6F•0x72-0x)

logic analyzer 2