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bus UART RX TX RTS CTS

Definition

UART is serial bus.

Specification

Signals
RX Receiving Line (In)
TX Transmitting Line (Out)
(RTS) Request to Send
(CTS) Clear to Send

Note: TX signal of the sender is connected to the RX signal at the receiver!

Baudrate

Baudrate is the same as frequency or bitrate in bit/s!

Common Baudrates:

Example

If a baudrate of 9600 bits/s is used with one stop bit and no parity (10 bit per byte) then the datarate would be 960 byte/s.

Protocol

UART uses serial transmission of 8 bits framed by start and stop bits.

       ___     ___ ___ ___ ___ ___ ___ ___ ___ ________
RX ---    \___/___X___X___X___X___X___X___X___X___/    ---
            S  b0  b1  b2  b3  b4  b5  b6  b7  pr   P

S: start bit,  b0-7: data,  pr: parity bit,  P: stop bit
Explanation

All operations of the UART hardware are controlled by an internal clock signal which runs at a multiple of the data rate, typically 8 or 16 times the bit rate. The receiver tests the state of the incoming signal on each clock pulse, looking for the beginning of the start bit. If the apparent start bit lasts at least one-half of the bit time, it is valid and signals the start of a new character. If not, it is considered a spurious pulse and is ignored.

Variants: Stop bits: 1, 1.5, 2
Parity: odd, even, none

Receiver Errors

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