Post 19 - Back from the dead (sort of)

21 Dec 2022

Task 24, Day 19, Hardware Hacking Wiggles go brr

Too many things going on and had to skip a couple days, but kept the streak going at least through answering some random simple questions. Now I have three days worth of AoC to catch up on though.

USART

Universal Synchronous/Asynchronous Receiver-Transmitter better known as serial communication, protocol using two wires, transmit and recieve. Without clock line for syncing communication devices need to agree to communication config, including:

• Baud rate - speed of comms
• Bits per transmission - normally 8 but could be something else like 16
• Stop and Start bits - without clock one device needs to send a signal to the other before it can send or end transmission
• Parity bits - used to detect and correct comm errors in transmission

Some USART include wires for Clear To Send (CTS) and Request To Send (RTS) to communicate to the other device if it is ready to send or receive. Need ground for maintaining voltage refs.

SPI

Serial Peripheral Interface protocol mainly used between microprocessors ans small peripherals like SD cards or sensors. SPI has separate clock (SCK) wire from data (DATA) allowing synchronous comms, faster more reliable. Clock tells receiving device exactly when to read the data line. Only one device (controller) allowed to send clock signals. For two way comms, two data lines are needed, becoming Peripheral-In-Controller-Out (PICO) and Peripheral-Out-Controller-In (POCI). For multiple devices all share SCK, PICO, and POCI lines, but controller has one Chip Select (CS) for each device to identify who should be transmitting/receiving.

I2C

Inter-Integrated Circuit protocol created to deal with drawbacks of previous two protocols. Uses only a Serial Data (SDA) line and Serial Clock (SCL) line. Instead of Chip Select it uses and Address signal over the SDA wire. Tells all controllers and peripherals which device is trying to communicate and who it’s trying to reach. Comms begin with a Start signal and end with a Stop signal to prevent talk over from other devices. Slightly slower than SPI, but faster and more reliable than USART while only using two lines. Address signal allows up to 1008 devices to connect to same lines and be able to communicate.

The Task

(Look into Salae Logic analyzing software)
Answer questions about USART, SPI, and I2C protocols and grab the flag.

Flag gotten, fun had. Should make time to watch John Hammond’s video of the task.