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by jacquesm 2970 days ago
The combined time is equal, why would it matter what the order is?

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.
2 comments
Stratoscope 2970 days ago
It doesn't matter that the combined time was equal. What mattered was that both operations completed before the next character was printed. The carriage return and the line feed could happen in parallel, but I'm pretty sure that carriage return could take longer than line feed, at least in the worst case when the carriage was near the end of the line. So if you did the line feed first, the next character could print while the carriage was still returning.

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.

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jacquesm 2970 days ago
I see what you're getting at. That the next character would start to be printed before the carriage return had completed with the sending side not respecting the fact that it had just sent a carriage return by waiting for a bit.

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.

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mark-r 2970 days ago
I remember a system that overprinted about 5 characters to black out a password after you entered it. Good times.

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

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jacquesm 2970 days ago
Hehe, security by obscure it y.

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.

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mark-r 2970 days ago
The head wouldn't start moving until it got the CR, and if the LF comes after it would have 2/10 of a second to traverse the page. If the LF comes first it would only have 1/10 of a second.
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