Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!ucbcad!ucbvax!ANDREW.CMU.EDU!mw22# From: mw22#@ANDREW.CMU.EDU (Michael Alan Wertheim) Newsgroups: comp.sys.apple Subject: Re: screen memory question Message-ID:Date: Mon, 15-Dec-86 10:47:34 EST Article-I.D.: andrew.MS.V3.18.mw22.80021110.clarion.ibm032.214.0 Posted: Mon Dec 15 10:47:34 1986 Date-Received: Tue, 16-Dec-86 21:07:53 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: University of California at Berkeley Lines: 29 There seems to be a lot of confusion regarding 40 and 80 column text. The original Apple II had three display modes -- 40 column text, lo res graphics, and hi res graphics. Each of these modes has two pages. Text and lo res page 1 occupy the memory from $400 to $7ff, and text and lo res page 2 occupy $800 to $bff. Applesoft programs normally reside in the page 2 memory. If you load a program that has some strings, rem statements, or data statements near the beginning, and flip the page 2 softswitch ($C055 I think), you will see the strings and rem/data statements along with a lot of other garbage, which is the tokenized form of your program. Also note that you can BSAVE a screen from page 1 or page 2, but you can BLOAD the image only back to page 2. An 80-column card in effect doubles each of the display modes by using page 1 from main memory and the corresponding page 1 from auxiliary memory. The 80-column text screen uses $400 to $7ff of main memory and $400 to $7ff of auxiliary memory. Page 2 is not used. Likewise, there is also an 80-column double lo res that uses the same memory and that can easily be accessed from Applesoft. This was covered in a past issue of Open Apple. If anyone's interested, I'll post a short summary of how to do this. Double hi res uses the memory from $2000 to $3fff in both main and auxiliary memory. I've heard that there is a double hi res page two that uses the memory from $4000 to $6fff in both main and auxiliary memory. Mike Wertheim (Carnegie Mellon University)