Lab
What 8N1 actually means
Every serial terminal asks for 8N1 and almost nothing explains it. It is three numbers: eight data bits, no parity, one stop bit. Change any of them below and watch the frame change shape.
Hover any slot for what it does. The thing worth noticing: data bits go out least significant first, backwards from how you write the number down — which is why reading a waveform off a scope feels wrong the first few times.
What this shows
8N1 is three settings, not one: eight data bits, no parity, one stop bit. That is the default on virtually every serial device, and it puts ten symbols on the wire for every byte you send.
The two extra symbols are structural. The start bit is a high-to-low transition that gives the receiver an edge to synchronise on, because asynchronous serial has no clock line. The stop bit returns the line to idle-high so that the next start bit is guaranteed to produce a transition.
Data bits go out least significant first, which is backwards from how the number is written down. Capital B, 0x42, leaves as 0 1 0 0 0 0 1 0.
Changing the format changes throughput and tolerance together. 8N1 costs ten bit-times per byte; adding parity or a second stop bit makes it eleven, which is 27% overhead instead of 20% and moves the last slot further from the synchronising edge, so the frame tolerates less clock error.
Common questions
- What does 8N1 mean in serial communication?
- Eight data bits, No parity, and one stop bit. It is the default frame format on almost all serial hardware. Including the start and stop bits, one byte occupies ten bit times on the wire.
- Why are serial data bits sent least significant first?
- It is a convention inherited from early UART hardware, where a shift register clocking out from the low end was the cheapest implementation. It means a byte on an oscilloscope reads backwards compared with how you write the number, which is why reading a capture feels wrong the first few times.
- How many bits does it take to send one byte over serial?
- Ten at 8N1 — one start bit, eight data bits and one stop bit. That is why 9600 baud carries 960 bytes per second rather than 1200: baud counts symbols on the wire, and two in every ten carry no data.