"stop bits"; was: NEC uPD7201 misfeature

It carries just as much information as the start bit. Bits do not necessarily carry information in the sense of anti-redundancy; for example, the high bits in the octets making up this email carry little-to-no information, since they're all the same, but they're still real bits just the same. I'm not sure what's "5-level" about it, but I think "just plain insanity" is overstating the case; it seems fair to me to consider it a kind of shorthand for "1.5 bit times". For reliable operation, receiving devices must accommodate a slightly short stop bit; otherwise, if the sender's clock is slightly faster than the receiver's, streaming characters back-to-back will produce phase drift and eventually a framing error. I don't know enough about most UARTs to comment on them in this regard, but I think I once saw documentation on one which implied that it was willing to tolerate receiving a character that was only (what the receiver's clock says is) only a little over 9.5 bit times long, because it samples in the middle of (its idea of) each bit time, starting half a bit time from the beginning of the start bit, and, provided the stop-bit's sample shows the correct level, it is immediately ready to accept a new start bit's beginning after that sample. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B