[RTTY] Print

[Kok Chen]

On Sep 30, 2008, at 9/30    7:50 AM, rick darwicki wrote:

> "Print you", vs CRT or LCD you ? Never changed my ribbon once.


Ribbon?  I am sure Guttenberg had never changed a ribbon either :-P

All kidding aside, the "print" statement in computer languages (like  
printf in C) are general enough to cover among other devices, the  
printer, the display, serial ports and computer files on a hard drive.

> CR or LF vs Enter ?

Now you are getting esoteric :-)

Strictly speaking, a carriage return will only return the carriage  
platen (or the print head, if the platen is fixed) of the mechanical  
device to type next at the leftmost position.

A CR by itself should cause an overprint of the existing line.  Very  
few software today will obey that.  But just 30 years ago when  
Teletype Corp Models 33 and 35 and IBM 2741 terminals were used as  
the console for computers, CR meant CR, not "newline" (which most  
RTTY software will translate a CR to).

Back then, CR-only was common behavior and was exploited by many text  
editors to create "bold" text by overstriking the word that you need  
to bold (the IBM 2741 will do that even with a non-fix pitched type  
ball -- it was the Rolls Royce of terminals).

LF on the other hand, will only advance (rotate) the platten, and  
moving to the next line of the type -- thus "line feed."  The  
horizontal location it types on next does not change from where it  
was on the previous line.

To move to the beginning of the next line, you will need to issue  
both a CR and an LF to a teletypewriter.  It is preferred to issue a  
CR first and then an LF -- this gives an extra 1/6th of a second (for  
45 baud Baudot) for the platen or type head to settle down after it  
executes the carriage return.

With the cheap and slow teletypes like the model 33 when operated at  
a higher 300 baud speed, we used to issue CR-CR-LF.  The extra CR  
does not change the position of the type cylinder, but gives you  
extra time for the type head to settle down.  If you didn't do that,  
the first character of a line that is being streamed can have a fuzzy  
appearance since the type head is struck while it is still settling  
down.

Scary thought -- some teenagers today may never have ever seen a real  
typewriter, much less a teletypewriter.

73
Chen, W7AY