Description: Apple IIc: 80/40 switch
Header: Apple IIc: 80/40 switch

 The 80/40 switch on the Apple IIc only sets a bit in memory. While a program
 can read this bit and use the setting in a decision to display 80 or 40
 columns, in practice, only a few programs, e.g. Apple Writer, take advantage
 of the switch in that way. In itself, the 80/40 switch does not force 80
 column firmware on or off; only a software command like Applesoft's PR#3 or
 PR#0 can do that.

 The 80/40 switch on the Apple IIc was designed for customers who use their
 television set as a monitor. A television set doesn't display 80 columns of
 text very legibly; 40 columns reads much better. Unfortunately, most Apple II
 software packages, written before the Apple IIc, don't check the bit set by
 the 80/40 switch.

 Because the bit setting is independent from the PR#3 command, programmers can
 use the bit set by the 80/40 switch for features other than 80/40 column
 display:

 10    TEXT:HOME:REM INITIALIZATION
 100   SWITCH = PEEK(49248):REM MEMORY LOCATION FOR CURRENT SWITCH SETTING
 110   VTAB 12
 120   IF SWITCH > 127 THEN PRINT "80/40 SWITCH DOWN":REM OR ANYTHING ELSE
 130   IF SWITCH < 128 THEN PRINT "80/40 SWITCH  UP ":REM OR ANYTHING ELSE
 140   GOTO 100

 For more info, see the two-volume Apple IIc (16K ROM) Technical Reference
 Manual, pages 5 and 77 of Volume I and page 128 of Volume II, or the
 one-volume manual published by Addison-Wesley, pages 5, 80, and 342.
 Apple Technical Communications


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