Notes

Asynchronous Serial Communication

USB = Universal Serial Bus

• UARTs = Universal Asynchronous Receiver-Transmitters

CDC = Communications Device Class

TX = Transmit Line

RX = Receive Line

Agreements between sender and receiver

• electrical(TX | RX | GND) agreement
• speed(timing communication) agreement
• logic(data format) agreement - both sides need to agree on what the bytes being sent mean, and in what order they are being sent.

<aside> 📌 Definition of asynchronous serial communication: The sender sends pulses representing the data to be sent at the agreed-upon data rate, and the receiver listens for pulses at that same rate.

</aside>

Both devices keep time independently, and either send or listen for new bits of data at an agreed-upon rate.

Serial Voltage Changes

RS-232 uses inverted logic, which means that a high voltage indicates a logic 0, and a low voltage indicates a logic 1.

Serial Buffers and Control of the Port

serial buffer: an area in a UART of all processors in memory where they store incoming data from the serial ports, so they can do other tasks while waiting for data to come in, and act on the data from the buffer after it comes in.

serial buffers are also called First-In, First-Out or FIFO buffers. Because as you read each byte, the byte is removed from the serial buffer.

<aside> ⚠️ Serial ports can only be controlled by one program at a time.

</aside>