[GreenKeys] [Bulk] Re: C-64 to drive Mdl. 15 TTY (and probablyothers..)

[Ralph Mowery]

Dave just made a mistake by saying FIGS when I am sure he ment to say LTRS.  That is assuming that the sender really wants to start out in LTRS instead of FIGS.

Some of the older machines may be slow and take some time to get back from the far end of the line. That is why it takes a couple of non printing charicters after the CR.  You can send as many CRs in a row as you want and most machines will be fine with that.  A few are setup to do a line feed after a CR, so many CRs will waste the paper.  That is why only two CRs are normally sent.

Most machanical machines do not have anything to tell it that it is at the end of the line or to advance the paper to the next line so the charriage gets to the end of the line and just bangs a hole in the paper.  By sending two CRs it makes sure the carriage gets at least one of them when sent over the radio circuit if a burst of noise jumbles one of them up.  Only one LF is sent to keep from wasting paper.   Then either one or two LTRS is sent to give the carriage time to get back if it is slow to do it when running at machen speed.  

Most of the computer terminals automatically send the cursor back to the left and starts a new line where the mechanicals do not.  It is very agervating to have to sit at the printer and mechanically hit the CR lever and advance the crank for a new line. 

The program I wrote years ago for an 8080 processor was set up like this.

It would count the number of characters sent on a line and after 65 or maybe it was 68 characters it would look for a SPACE between words.  If it got a  space, it would do the CR CR LF LTRS LTRS to end the line and start a new line.  If there was no space, it would wait for character 72 (the normal line length of most machines) and then force the end of line sequence.

While not much use to most people, but I did it to edit the RTTY PIX.  I had a way of telling the computer to go to the  pix mode (just my term for the rtty pictuers) by using some ASCII characters on the keyboard that had no Baudot equal.  When in this mode, it did not count the characters or do any end of line sequence.   That way for the pix that are over printed or run to the end of the line you had to actually enter the CR or LF when it was needed and also the LTRS twice for the end of the line.  

One other thing, about half the machines have the FIGS case of the J and S reversed.  That is you may send a Bell or ' when you ment the other to come out on the receiving machine.  The program I wrote would send both of them out if either was pressed.  

I am sure that you will also have a buffering in the computer program so you can type faster than 60 wpm  so you do not over run the mechanical machine.

Make sure you start off every new transmission with the cr cr lf ltrs so the printer will always start off fresh.

If you have never used a mechanical printer then you are not aware of the things it will do.  There may be some other minor things I have left out.

73 de ku4pt

  ----- Original Message ----- 
  From: drlegendre . 
  To: Dave Horsfall 
  Cc: Greenkeys 
  Sent: Friday, September 04, 2015 3:03 AM
  Subject: Re: [GreenKeys] [Bulk] Re: C-64 to drive Mdl. 15 TTY (and probablyothers..)


  I think I've understood the reason to send the LTRS shift (not sure why +two+ times, but whatever) as if the last shift is FIGS it leaves the remote machine in FIGS. This would mean the remote typist might accidentally send FIGS chars when they believe the machine is in LTRS shift. 


  Thus the courtesy, correct? 


  Also, sequential CR chars have no effect, other than to busy the line, once the first CR makes it to the other machine - right? Multiple LFs would be another matter, then..


  As far as the char-per-line count, it never struck me that the receiving machine wouldn't be able to sense the EOL limit and make a CR/LF (wrap the text) when needed, like any 'smart' terminal should. So on the driver side, I need to keep track of the number of (printable..) chars since the last CR/LF - and send a CR/LF pair when the length exceeds the limit - do I have that right? 


  Any further comments are welcome!


  This is all great info, and very helpful. It's not all that easy to get all this stuff figured out when I don't actually have an M15 to work with. But I think that situation changes this weekend.. the M15 should be here on Sat. or Sun. afternoon.


  I'll post pics. ;-)


  -Bill

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