Re: [stella] vcs.h: Incorrect constants?

Subject: Re: [stella] vcs.h: Incorrect constants?
From: "John Saeger" <john@xxxxxxxxxxx>
Date: Sun, 28 Jul 2002 17:22:22 -0700
Holy bitmask batman!  A bug in Bensema's vcs.h!?  It just goes to show you.
Never trust a constant that isn't all caps.  ;-)

John


Eric Eid wrote:

> I had some difficulty adding uses for the difficulty switches to my Euchre
> game yesterday.  I thought sure that I had the proper bit masks.
>
> I looked at the vcs.h I picked up at
http://www.io.com/~nickb/atari/doc/vcs.h
> and found this:
>
> ;
> ; Switch B equates
> ;
> SWCHB   =  $0282
> P0_Diff = $80
> P1_Diff = $40
> Con_Color  = $08
> Con_Select = $02
> Con_Start  = $01
>
> It's also the same in Glenn Saunders' proposed standards constants file,
> vcsc.h
(http://www.biglist.com/lists/stella/archives/200111/msg00427.html):
>
> ;DIFFICULTY SWITCHES
> P0_Diff = $80
> P1_Diff = $40
>
> In the ASCII version of the Stella Programmer's Guide
> (http://www.io.com/~nickb/atari/doc/stella.txt), the section on SWCHB
reads
> as follows:
>
>   4.1 Port B - Console Switches (read only)
>      Port B is hardwired to be an input port only that is read
>      by addressing SWCHB (HEX 282) to determine the status of
>      all the console switches according to the following table:
>
>           Data Bit  Switch         Bit Meaning
>           D7        P1 difficulty  0 = amateur (B), 1 = pro (A)
>           D6        P0 difficulty       0 = amateur (B), 1 = pro
>           (A)
>           D5/D4          (not used)
>           D3        color - B/W    0 = B/W, 1 = color
>           D2        (not used)
>           D1        game select    0 = switch pressed
>           D0        game reset     0 = switch pressed
>
> It looks to me like the values of P0_Diff and P1_Diff are switched around
in
> vcs.h.
>
> Am I reading this correctly or is there something I am missing?
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