Basic help/where is zork?From: ag971
Date: 07/30/89-09:10:11 AM Z
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From: ag971 Subject: Basic help/where is zork? Date: Sun Jul 30 09:10:11 1989 Help! I have an Atari 800 XL, I'm writing in Revision C Basic (because B has a BUG, and A is less powerful). My question is: how could I have High Resolution Graphics on the first 1/2 of the screen and text on the bottom half of the screen simultaneously? Also--where could I find the Zork Trilogy for my computer? Thanks a lot. John Rowland ** Answered by DOUG WOKOUN (aa384) on Fri Mar 31 20:32:11 1989 ** Basic REV.A also had a bug, just like REV.B The Rev. B bug scrambled programs when a multiple of 256 bytes were inserted into a program...this was CREATED by Atari while trying to fix a bug in Rev.A where deleting 256 bytes from a program cause a crash. To get a Display List with mixed graphics modes... First you need to find out where the Display list is.... DL=PEEK(560)+PEEK(561)*256 The first three bytes at location DL are to move the screen down...(112) The next three bytes are a LMS (load memory scan with the graphics mode and screen memory location) 79 is the LMS for gr.8 and the next two bytes are the LSB,MSB for the display memory. for each scan line of Gr.8, use a 15 for that byte in the display list....then to switch to gr.0, use another LMS (66) and the new memory location....you cannot have more than 4K of screen memory without a LMS then, put several lines of gr.0 (2) and top it off with a jump and wait for vertical blank (65) followed by the address of the start of the display list. To map this out: Start > 112 112 112 79 LSB (screen memory) MSB (screen memory) 15 15 15 ... until you get halfway down the screen... 95 of these should do it. 66 LSB (screen memory for Gr.0) MSB (screen memory for Gr.0) 2 2 2 (12 of these to get 2... to the bottom) 65 LSB (START) MSB (START) You can get more information from Compute!'s Mapping the Atari which has an excellent section on Display List Interrupts. There are several DL codes for blank scan lines and other graphics modes unavailable with BASIC. Try B&G for Zork and other software . It is about the only place left locally. Thanks for asking. Doug Wokoun aa384 Atari SysOp
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