Very old filesystems didn't track file sizes in bytes, just blocks, so a literal EOF byte was needed to know where to stop reading in the middle of the last block of 128 bytes or so.

So any device that uses it usually requires a special adapter that converts CR-LF to LF-CR otherwise the printer could be damaged and buffers input while the printhead lock the linefeed.

The device was to my knowledge not very popular, incredibly old and irreplaceable as part of a legacy application written for an old 8bit computer system.

http://hans.presto.tripod.com/scan/teletype/28_02.html

"Dependable carriage returns with only one carriage return and one linefeed signal" at 100 wpm.

Now I'm curious :)

I don't have a teletype handy though, I'm sure other HN'ers do.

We always played it safe anyway, by punching CR LF RUBOUT at the end of each line on a paper tape. The RUBOUT added a bit more delay before the next character was printed, so you could feel sure that it would print at the correct position.

From what I remember most TTY drivers would automatically insert an appropriate delay after a CR because the LF is optional, you can happily overprint a line if you want.

The NUL character was useful for inserting a delay into the serial stream.

And in sync links (not TTY's those were mostly async with start and stop bits, more like HDLC style stuff) those nuls were mandatory, you had to send something.

* http://jdebp.eu./FGA/dos-character-26-is-not-special.html

And SUB was ASCII's equivalent of U+FFFD.