Talk:Basis 108
More Basis 108 Keyboard Information
I'm currently studying the Basis 108 keyboard, and I'd like to upload my findings to this wiki.
Right off the bat, there are actually two versions of the Basis 108 keyboard. The keyboard currently documented on the page is what is called the "black keyboard" because of the color of the key caps. There's another model of keyboard referred to as the "white keyboard," again based on the color of the key caps. I believe that the white keyboard is the later keyboard, as the PCB is labeled as "A2." The earlier black keyboard is labeled "A1" on the PCB. Both versions have de-bouncing issues, and there are home-brew solutions passed on through the user groups to fix the problem by developing a separate board that replaces IC3 on the keyboard's PCB. IC3 can be found right above the key switch used by the F7 key.
Another difference between the different models of keyboards lie within the encoder electronics, particularly the IC3 chip I mentioned earlier. Later white keyboards use the CMOS 4051 analog multiplexer, hence the white keyboard is also known as an "analog" keyboard. The 4051 was also socketed, so it was removable, which some owners did in order to replace it with de-bouncing circuitry. The earlier black keyboard replaced IC3 with a TTL 74LS151 multiplexer, hence the name "digital keyboard." The 74LS151 was originally soldered directly to the PCB. Later productions of the black keyboard has the 74LS151 socketed.
Here's some other bits of information that makes the Basis 108 and the keyboard special. Unlike many of the other Apple II computers, the Basis 108 was the only system capable of handling different character sets. The motherboard has a 2532 EPROM that handles character generation. There are two versions of the EPROM: 46-3 (sent out with the German systems) and 46-4 (sent out with the American systems.) The keyboard didn't spit out ASCII codes like the Apple II and clones. Instead, the keyboard sent out scan codes, which the character generator then transcribed to depending on the EPROM. The character sets are:
- Set 0 - Standard Apple II
- Set 1 - German ASCII (43-3) or ASCII (43-4)
- Set 2 - ASCII (43-3) or German ASCII (43-4)
- Set 3 - APL
- Set 4 - Full German ASCII (43-3) or Full ASCII (43-4)
The German and American models had different key caps, matching the language of its target market. Other than that, the rest of the keyboard was the same.
Unlike the Apple II series and virtually all of its clones, the Basis 108 keyboard's strobe signal is inverted. The keyboard also powered off the +12VDC line, which was then stepped down to +5VDC through a regulator. The RESET sequence is LEFT-SHIFT/RIGHT-SHIFT/CONTROL keys at the same time (similar to what would become CTRL-ALT-DEL, hence the keyboard had to use N-key rollover. The keyboard also supports "Alphalock" and "Shiftlock." If the LOCK key is pressed with the CONTROL key, it switches the keyboard to alphalock, meaning all alpha keys will be uppercase. If the LOCK key is pressed by itself, the keyboard switches to shiftlock, meaning all keys will generated its uppercase equivalent, including the numeric keys. Specialized software can take advantage of the keyboard's "interrupt mode" feature. By enabling the feature through a softswitch ($C008 OFF, $C009 ON,) each key press generates an interrupt.
