CMDSEN@PRIMEG.WEEG.UIOWA.EDU (11/02/90)
I applaud Morgan Davis' proposal for a standard of using the 60hz signal on
a II+. $c060 maybe be the appropriate data address to use, but I want to
consider some alternatives. I need to consult some older literature at home.
Namely, the 'Micro' magazine article on using the 60Hz signal for a software
clock (connect to 6502? pin for interrupts @60/sec) - a cheap clock, even if
it has to set each bootup!. Also Don Lancaster's 'Enhancing the Apple II',
vol 1 (or vol 2 if it ever was published, never saw it!) may use this signal
for some purpose and provide an alternative address to use. Both are single
wire IC to IC connections. Interrupts for timing are not a bad alternative
to polling $c060 in my opinion. The problem is ensuring SEI is always the
default on a II+ (I think it is) so the interrupts don't interfer when not
used. Can the address used for VBL polling on the IIe/IIc be used? It would
make software writing easier if a common routine could be used for all 8-bit
II's :-)
My weak objection to using $c060 is I already use it (or used to). Why? Just
like $c063 is used to detect shift-key, I use $c060 to detect ctrl-key in my
keyboard drivers. (Pin 24 on encoder connector for shift key, pin 3 for ctrl
key; to pins 1 and 4 of the IC in front of the game I/O port). Useful for
using ctrl-1 ... ctrl-9, ctrl0, ctrl: ctrl- to generate special characters
not available on keyboard (or shift-ctrl keys even!), detect 'real' ctrlU and
ctrlH from left and right arrows, etc. Anyway, $c060 is convenient and the
ctrl-key mod does not interfere with normal cassette port usage (unless the
ctrl key is held DOWN), or with the use of the cassette port for a 4th game
button, as I believe some old 2-player games did. (My paddle-addapple alludes
to such use.)
So in summary, is there another address already decoded in Apples address
space that could be used un-obtrusively instead of $C060?
--Steve Nelson (cmdsen@primeg.weeg.uiowa.edu Internet)
(cmdsenpg@uiamvs.bitnet Bitnet )