Apple II text encoding, how?

Retronaut

Retronaut

New Tinkerer
May 11, 2025
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I need to write up some info on how the Apple II encodes text. I read in a Wikipedia article that it uses 7bits to encode a 64 character set. Well, we only need 6 bits, to define 64 values. So how do the other 64 values in a 7bit value get used? Also, it says the 8th bit is used as a toggle between modes. All in all the article is not quite clear enough. Does anyone have a link to a PDF on this subject with a clearer explanation?
 
N

NJRoadfan

New Tinkerer
Feb 6, 2022
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The character sets and values are here: https://en.wikipedia.org/wiki/Apple_II_character_set

"Normal" text requires the 8th bit to be set. There are no extended characters on the II/II+ (IIe/c have lowercase here), so setting the 7th bit just duplicates the set. To use the "alternative" set (inverse and MouseText if you have a IIc), instructions are here: https://en.wikipedia.org/wiki/MouseText

Its why printers are typically jumpered to ignore the 8th bit as you would print the wrong characters out, particularly from AppleSoft BASIC.

Also: https://retrocomputing.stackexchang...e-e-have-two-sets-of-inverse-video-characters
 
Retronaut

Retronaut

New Tinkerer
May 11, 2025
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Ok, so to be clear. Referring to the image below (thanks Wikipedia!)

If I set Bit 8 to 1, and bits 1-6 to 0-64, then I would see @ABC.. etc from the THIRD block of characters along.
If I also set Bit 7 to 1, then I would use the 4th block of chars, shown here as exactly the same as the 3rd block. But... this would be mouse chars on Apple IIc?
And if I set Bit 8 to 0 and Bit 7 to 0 I would use the inverse char set in block 1
And if Bit 8 to 0 and Bit 7 to 1, then I would be able to select a char from block 2, the Flashing text?

Apple_II_character_set.gif
 
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