Grumpy_Mike:
The start bit is the space state and the idle or other part is the Mark state. The Mark is always the undriven state of the line and the space is the driven state. When logic came in the undriven logic state of an input is a logic one.
A fault is said to occur when the line is in the space state for longer than a character time. This is known as being "spaced out". Perhaps it is the origin of the phrase that has such a diffrent meaning today.
Well before RS-232 sprung onto the world the old teletype world used simple on/off current loops for the signaling levels using 20ma or 60ma level. The idle (stop) condition was current flowing and start/space/data bit false state was current off. If a line break caused the line to stay at current off, it was also called 'running open' as the teletype would just continuously cycle thinking blank characters were being sent and would never enter the latched up idle state, making a very distinct sound.