Above the keyboard of my Apple IIc there are two buttons that say "80/40" and "Keyboard".
On my machine, they both kinda feel broken. When I press them, they recede into the case and remain there for a while. Eventually they reset to their original position; but pressing them feels sort of like shoving something between two couch cushions.
What should these buttons do? How are they used? (I assume the 80/40 button has something to do with enabling 80-character mode.)
On the International version Apple IIc the keyboard switch swiched between a country-specific layout and and a standard U.S. layout. On the USA version it switches between the standard QWERTY and a Dvorak layout. (This was not so much a desired feature as a side effect of having to build the European version with a keyboard switch; putting a Dvorak switch on the USA version thus came "for free," and was in fact cheaper than doing a second case mold.) The layouts are given in Appendix G (p. 366) of the Apple IIc Technical Reference Manual.
Like caps lock, this switch toggles a setting in the keyboard controller and is not seen by software running on the Apple IIc.
On machines with older keyboard ROMs the Dvorak layout is slightly different; the older layout and further information are given in Apple IIc Technical Note #4, found in this document. (Keep in mind the keyboard ROM is separate from the system ROM and the system ROM version does not necessarily indicate what keyboard ROM version you have.)
There have been claims that adding the Dvorak layout to the USA version was to save having two different cases, but the reference given on that page doesn't check out.
Unlike the keyboard switch, the 80/40 switch is read only by software, and it's up to the software to decide when to check it and do something (or not) based on its current setting. This is explained on page 5 of the Apple IIc Technical Reference Manual:
Not all programs check this switch. Even programs that do check the switch may do so only when the program first starts up. If that is the case, changing the switch position while the program is running will have no effect on the program's display.
Further, some programs (e.g. the ProDOS system utilities) will use 80-column mode regardless of the switch settings.
I just did a couple of checks and found that everything I booted ignored the switch. These tests were done on a IIc with the original ("version 255") ROM.
If you wish to check the status of 80/40 from your own software, this can be done by checking bit 7 of location $C060; 1 indicates the switch is down. (Table 4-1 in the TRM has full details.)
Despite looking different externally, the reset, 80/40 and keyboard switches are standard keyswitches as used on the rest of the keyboard: reset is a momentary-press switch and 80/40 and keyboard are locking switches like caps lock.
The older (pre-Alps) keyswitches seem often to have problems as the age, feeling slightly "crunchy." The locking switches in particular seem to have problems; if your caps lock doesn't easily switch from on to off, having the older keyswitches is probably your main issue.
That said, the particular design of the 80/40 and keyboard keys probably exacerbates the problem, since unlike the other keyboard keys they have much greater contact with and interaction with the case itself.
According to the Wikipedia article:
The keyboard layout mirrored that of the Apple IIe; however, the “Reset” key had been moved above the “Esc” key. Two toggle switches were also located in the same area: an “80/40”-column switch for (specially written) software to detect which text video mode to start up in, and a “Keyboard” switch to select between QWERTY and Dvorak layout—or between US and national layout on non-American machines.
As stated in the reference above, the "80/40" key is a signal to software that is aware of it, but the software has to know to care about it, and the "Keyboard" switch seems to be intended to switch keyboard layouts.
There are also references to this funcionality where it is mentioned that the number of columns on screen can also be changed in software with ESC-4 and ESC-8 (presumably to set 40-column and 80-column modes respectively).
Though Thomas Jager is correct in his answer, I'll add a bit about the practicality of those switches for a USA model.
The 40/80 column switch never appeared to do anything in any of the software I used. Though it has been years since I used a //c, I think it might have set the display mode at startup (i.e. pushed in, the computer would boot in 80 columns). Pressing the button during runtime did nothing since it didn't trigger any interrupts or code in the Apple, it only would set a flag in memory that something could read. I'm sure there is something out there that used it, but I'm not aware of anything in particular.
The keyboard switch was interesting, but only for those who believed that the Dvorak layout was more efficient that Qwerty. As for me and my friends, we'd experiment with it but since the key caps on the //c did not have the alternate layout printed on them nobody that I knew ever really pursued it. I feel like it takes a good week or two to get used to a new layout and several to become proficient. To be honest, I think it was a neat feature but hardly (if at all) used. Perhaps if Apple made it easier to show the Dvorak map (either by dual-printed or easily swapped key caps).
My 2¢.
