Re: Hopefully last dumb newbie question.

[spec@vax2.concordia.ca (Mitchell Spector)]

In article CUTjefbla@bconnex.net (Jeff Blakeney) writes...

>On Thu, 04 Jun 1998 13:43:07 -0500, Slick <Slick_RCBD@hotmail.com>
>wrote:
> 
>>Now the question. What exactly does the Alternate Display Mode DA do? I
>>think it has something to do with the secondary text screen (Address
>>$800-C00 on earlier models), but am not sure. None of the books at my
>>library have anything about it. I do know about the shadowing to banks
>>$e0 and $e1, and have looked at assembly language programming on the
>>IIGS. I just never had the money to buy ORCA or APW. I've used the Hyper
>>C (ProDOS 8, and free) assembler to write programs.
> 
>If I remember correctly, text page 2 doesn't get shadowed or the
>softswitch for changing to text page 2 doesn't work or something like
>that.  The Alternate Display CDA allows you to enable or disable
>another shadowing routine, which is slower than the hardware
>shadowing, but allows certain older 8 bit programs to use text page 2
>so that they will work correctly.

    Another nice feature about the ROM 3 IIgs is there is hardware
shadowing for text page 2 built-in. If you run a program that uses
it (example: joystick calibration in Goonies) it will automatically
activate, and it doesn't slow down the computer. In that sense the
ROM 3 is more compatible with 8-bit software.

>If an 8 bit program crashes or doesn't run correctly, try enabling the
>Alternate Display mode and try it again.  It just might work.

    Usually you'll see a screen filled entirely with the number "2".
I'm not sure if this is a coincidence or Apple had it purposely used
to give a hint to the user, instead of random garbage on the screen. :)

Mitchell Spector
spec@vax2.concordia.ca