On Sat 06 Apr 2019 at 14:04:22 +0200, Mia Magnusson wrote: > Den Sat, 06 Apr 2019 12:07:25 +0200 skrev Rhialto <rhialto_at_falu.nl>: > > On April 5, 2019 6:08:01 PM GMT+02:00, Francesco Messineo > > <francesco.messineo_at_gmail.com> wrote: > > > > >https://en.wikipedia.org/wiki/PETSCII > > > > Note that that page contains a lot of nonsense regarding which > > characters are valid. See the discussion page. Someone should really > > correct it now. > > Side track: > Are/were the terms "shifted" and "unshifted" really a thing, or is it > something that were invented by whoever wrote that parts of the > Wikipedia article? No, those terms were probably invented by that article's author. The terms usually used were something like "graphics mode" or "uppercase and graphics mode", versus "lowercase mode" or "upper/lowercase mode", or obvious variations on that. Later with the Basic 4.0 machines possibly even "text" vs "graphics", because switching between the modes changes the spacing between the lines. In text mode the screen is "stretched out" by putting 2 pixel lines of spacing between text lines. That article seems to have been based on what you see if you do something like PRINT CHR$(123), which is misleading. It should be based on ASC("X") for the various characters one is interested in. Then you clearly find that PETSCII follows the original 1963(?) uppercase-only ASCII, and that they set the high bit for all extra (graphical) characters. On the original chicklet keyboard as pictured you can even see why the graphics characters have the sometimes weird codes they have: they make (somewhat) sensible patterns on the keyboard. Where SHIFT directly translates to +128 on the PETSCII code; I think I remember it is literally like that in the ROM code. (ASC("shift-A") turns out to be 193 = 128 + 65, not the 97 as shown in the first two images) > Re correct the page: Where to start? It's kind of a mess that would > benefit from a more or less complete rewrite. That is why I haven't attempted it myself :-( "Some PETSCII codes cannot be printed and are only used for keyboard input (e.g. F1, RUN/STOP). " is also misleading, because there are lots of control codes that do nothing when printed. But you can certainly put them in text strings in your program. In "quote mode", RUN/STOP is (of course) an inverse C. > A few things spring to mind: It states that the VIC 20 font is the same > as the PET font, even though the pound sign replaced another char. The > talk page incorrectly states that this change happend with the C64. I may have misstated that (or being imprecise). In any case it is the backslash which was replaced with the pound. > Re the disussion of why Commodore did chose upper-lower case as they > did needs some more background. > > Noteable is that PET is the only one of the three "1977 computers" to > have lower case at all. APPLE II and TRS-80 only had upper case! (Well, > Apple II had a hires mode so you could roll your own lower case but > then the display would be rather slow). > > Lower case weren't that common at the time. Digitals VT50 terminal > (july 1974) only had upper case. The VT52 added lower case (september > 1975). The well-known "cheap" Lear Siegler ADM-3(a) terminal also had only uppercase; lowercase was an option. https://en.wikipedia.org/wiki/ADM-3A > Btw the physical layout of the PET business keyboard is the same as the > Digital "Decscope" VT50/VT52 terminals. > > https://en.wikipedia.org/wiki/VT52 > > According to the "DECscope Users' Manual" the VT52 has both a > upper+lower case mode (default) and a upper case + graphics mode, much > like Commodore did. It seems like this was done the same way as in the > first PET, with upper case staying at the same positions and lower case > being replaced with graphics chars. > > http://bitsavers.trailing-edge.com/pdf/dec/terminal/vt52/EK-VT5X-OP-001_DECscope_Users_Manual_Mar77.pdf Ah interesting, I wasn't aware of that! -Olaf. -- ___ Olaf 'Rhialto' Seibert -- "What good is a Ring of Power \X/ rhialto/at/falu.nl -- if you're unable...to Speak." - Agent Elrond
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