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Every sub-step is one bit. The line idles at mark; the start is one bit at space and the stop returns to mark.

Settings

The window shows the resulting format, for example 8N1.

The idle level

On a micro pin, mark is the high level. Pick low to read an RS-232 line drawn as it looks on the cable, which is inverted.

Character fields

Errors it detects

Every problem appears twice: in the field tooltip, explained in a sentence, and in the status box, boiled down to a two- or three-word label.

The summary

Each transmission is summed up in one line: how many bytes it has (5 B), and whether it was truncated or whether what is there is a BREAK of N bits at space.
A line entirely at the same level is not an error: it is a line you have not drawn on yet, or one that is idle, which looks the same.

How to start

With nothing drawn, the status box explains:
No character yet. The line idles high: pull it low for one bit as the start, then write the data bits, least significant first.