On Creed and Telex it is proposed to make use of escape characters, and this appears to be a very satisfactory solution to the problem. On Teletype, however, it is proposed to use non-printing characters (XOFF etc). Since it is clearly desirable to have a printed record that a deletion has been made, this leads to the proposal made in Secion 5.1 that the system should respond to XOFF and RUBOUT by printing something suitable. This seems to me to make a demand on the system that is unnecessary and I am wondering whether it would not be better to make use of a printed escape character on Teletype in the same way as on Creed and Telex. The escape character could, for example be @.
In P.D. 17, BREAK was proposed as providing an emergency return to command status, and other control signals (e.g. ALTMODE) were provided for controlling public and private systems. A new proposal for BREAK is as follows.
The function of BREAK should be to cause the computer to abandon any output which is going to the console, and to put the line in read status (after typing *** BREAK); that is to say, BREAK means "listen to me". The system will then remain in listening status for a short time (say 3 seconds), and if within that time any other control or other character arrives, the program will be resumed as if the character had arrived in the normal way. If no character appears within the waiting time the system will put the user into command status.
28 September 1966
Copyright © 1966 University of Cambridge Computer Laboratory. Distributed by permission. Thanks to Barry Landy, Roger Needham and David Hartley for giving permission to distribute these documents. Thanks to Barry Landy for lending me the paper document from which this was scanned. Any typographical errors probably arose in the course of OCR.
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Teletypes and Character Equivalences (no date or author given)
Next Planning Document: 19. A proposal for control signals and break, JCV, 8 October 1966
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