Talk:PETSCII: Difference between revisions
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Also, in the very first PET model, the screen codes for upper and lower case letters were swapped. So if you turned on lower case mode, your upper case letters remained on screen as they were, and to get lower case letters you had to press shift. Presumably because that was inconvenient, the character generator rom was changed, and that meant that when you changed into lower case mode, your existing on-screen uppercase letters became lower case (and some graphics became upper case letters), as it is known also on the 64. |
Also, in the very first PET model, the screen codes for upper and lower case letters were swapped. So if you turned on lower case mode, your upper case letters remained on screen as they were, and to get lower case letters you had to press shift. Presumably because that was inconvenient, the character generator rom was changed, and that meant that when you changed into lower case mode, your existing on-screen uppercase letters became lower case (and some graphics became upper case letters), as it is known also on the 64. |
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Going from PET to 64, the backslash was changed into a pound symbol |
Going from PET to 64, the backslash was changed into a pound symbol. |
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See lots of docs on the CBM Hackers site, http://www.zimmers.net/anonftp/pub/cbm, some of which was contributed by me (Olaf 'Rhialto' Seibert). |
See lots of docs on the CBM Hackers site, http://www.zimmers.net/anonftp/pub/cbm, some of which was contributed by me (Olaf 'Rhialto' Seibert). |
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Revision as of 10:43, 25 June 2007
Terminology
Instead of "shifted" and "unshifted", the two modes were commonly called "lowercase" (or sometimes "business") and "graphics" mode.
Also, since the shift key sets the high bits in the character, the way you mention the repeating characters is the wrong way around. Normal characters are 0x20-0x5F and with shift, 0xA0-0xDF. It is the others who were repeats. The reason for the repeats is that the PETSCII characters all map to 128 different "screen codes" (in the video memory) and they don't map 1-to-1, but the conversion code didn't care about that. In screen codes, the high bit is used for reverse video. In the keyboards after the first one, there were fewer keys, so the nice regular mapping of the shift key to the high bit was partially lost.
Also, in the very first PET model, the screen codes for upper and lower case letters were swapped. So if you turned on lower case mode, your upper case letters remained on screen as they were, and to get lower case letters you had to press shift. Presumably because that was inconvenient, the character generator rom was changed, and that meant that when you changed into lower case mode, your existing on-screen uppercase letters became lower case (and some graphics became upper case letters), as it is known also on the 64.
Going from PET to 64, the backslash was changed into a pound symbol.
See lots of docs on the CBM Hackers site, http://www.zimmers.net/anonftp/pub/cbm, some of which was contributed by me (Olaf 'Rhialto' Seibert).
Reasons for CBM to 'invent' PETSCII
This would be a more interesting and useful article if anyone could explain *why* Commodore chose to invent their own character set. In 1977, it's not like they were trying to lock people into only buying their peripherals from Commodore! --Wtshymanski 19:35, 19 Apr 2005 (UTC)
- Good question/comment! My best bet (in fact, a bet I'm quite sure I would earn a little money on, had anyone bothered to bet against it) is that CBM did this to allow for the excellent (IMNSHO) block graphics extension to regular ASCII. They were thus able to alleviate, to some degree (or at least, they thought so) the lack of bitmap controllable graphics and user definable character set of the PET range. Using those graphics chars, some reasonably decent looking 'arcade games' (for the era) were actually made for the PET. :-)
- As you might know, Atari also 'invented' a set of block graphics chars for their own 8-bit home computer family (different chars from CBM's, of course...). --Wernher 00:10, 20 Apr 2005 (UTC)
- So there---done it (added to the article the (most?) plausible reason for PETSCII to be invented, that is). :-) --Wernher 01:00, 20 Apr 2005 (UTC)
- A little dangerous, in my opinion; we're speculating, do we have a cite for this theory of the PETSCII character set? It's not apparent to me why they didn't just use the 8th bit set characters to extend the character set, as did the IBM PC and even the Osborne 1, where printable characters with the 8th bit set came out underlined (which looked way cool in WordStar) and non-printable characters were block graphics. --Wtshymanski 02:20, 20 Apr 2005 (UTC)
- Yes, we're speculating, which is why I wrote "...may be one reason...". I think the current educated guess, stated very carefully, is OK. As for why did they use this scheme and not any specific one out of a range of alternatives, I think that would be a little beyound answering the basic question of why they in fact invented a proprietary char set as such. But, absolutely, a very interesting question! I'd love to have some CBM engineer(s) give a recollection of those matters from the early days of Commodore! :-)
- BTW, I'm not sure whether a single one of the other extended/variable-ASCII charset articles have any mention of why their specific version got the way it is, and what other alternatives they considered (if any) and, if relevant, why they did or didn't import parts of other charsets or charset schemes. I have an idea that such information isn't the easiest one accessible; some times because none of the originators remembers (or, even, is at all alive), and/or that the documentation is non-existent. --Wernher 03:06, 20 Apr 2005 (UTC)
- I don't know if we *want* to see a complete history of ASCII - there's tons of stuff on the Net, any search with "Bemer" and "ASCII" will turn up lots of documents; I once found a .PDF file (which I don't have on this machine) that went into amazing detail about the history of heated discussion over the assignement of the codes in ASCII, which exceeded even my appetite for trivia. Till we get better data (hopefully some day), your more cautious re-write will be I think sufficient. I wish we *knew*, though...--Wtshymanski 04:00, 20 Apr 2005 (UTC)
- BTW, I'm not sure whether a single one of the other extended/variable-ASCII charset articles have any mention of why their specific version got the way it is, and what other alternatives they considered (if any) and, if relevant, why they did or didn't import parts of other charsets or charset schemes. I have an idea that such information isn't the easiest one accessible; some times because none of the originators remembers (or, even, is at all alive), and/or that the documentation is non-existent. --Wernher 03:06, 20 Apr 2005 (UTC)
- Peddle claims the inclusion of card suit symbols was due to the fact that one of the things that was on his specification list for the computer was an item that said that people should be able to easily construct card games with it.
I rewrote this sentence, but I wanted to highlight it here. Scary stuff. I hope I preserved the meaning. 82.92.119.11 21:43, 1 May 2006 (UTC)