From Paul.Williams@rrds.co.uk Sun Jan 10 23:27:55 1999 Date: Thu, 07 Jan 1999 15:30:27 +0000 From: Paul Williams To: Richard Shuford Subject: ansi_dec_controls_news.txt Dear Richard, Happy New Year. At the moment I am working on two documents for my terminals web site . They will explain: 1. How the standards ECMA-35 (character code structure) and ECMA-48 (control functions) relate to Digital's VT series of terminals. 2. How Digital has made use of the private extension facilities (eg. using ESC 7 and 8 to save and restore the cursor). I've been using Dejanews and your site to investigate how broad a coverage to give these documents, ie. to see what questions people have asked in the past. I believe there are two mistakes in ansi_dec_controls_news.txt that you might wish to correct, even though I'm several years late in joining the thread of conversation! ________________________________________________________________ 1. Private extensions to parameter strings for control sequences A post from James Carlson (about line 1020) explains: : "CSI ? 2 ; 4 h" is equivalent to "CSI ? 2 h CSI ? 4 h". The flags : (like the '?' character) are global within a single CSI sequence. and then, : the '?' flag can appear anywhere. For example, this is a sequence : equivalent to the one above, even if it is a bit strange looking: : : CSI 2 ; ? 4 h Although his first example is correct, the second example is not allowed by ECMA-48, which says that the use of '?' in any position other the first character of a parameter string is reserved for future standardisation. The same rule applies to the other "private flag" characters, '<', '=' and '>'. Of course, standards change over time and if terminals actually allowed the second example then we might just add the caveat that this construct is not recommended even though you can get away with it. However, I've tried this sequence on a VT320 and a VT420 and it doesn't perform any changes to either ANSI or DEC private modes. I was pleased about this because I have found the VT320 to be very compatible with ECMA-48 so far, although I appreciate that the behaviour of terminals in error conditions is not specified by this standard and could perhaps include partial execution of this erroneous sequence. ______ 2. ECH On line 1170 there is a small typo where it says that the Erase Character (ECH) sequence is invoked by the codes: Esc yy X which should say "Esc [ yy X". In fact this paragraph is almost identical to the one around line 780, so could perhaps be removed or made identical to that one. _______ Trailer Richard, do you get lots of email from people asking you for specifications of terminals? I was just wondering, because I've started receiving more mail now, and my access logs show that many people arrive at my site by typing "vt100" into Altavista or Yahoo. I even had an email from one person who wanted me to tell him how to write a terminal emulator! I wrote back suggesting that he shouldn't. Are you still at UT? Regards, Paul -- Paul Williams Racal Radar Defence Systems Ltd, Principal Engineer Manor Royal, Crawley, West Sussex, RH10 2PZ. Tel: +44 (0)1293 644540 Fax: +44 (0)1293 542812