Subject: Re: [stella] [MARIA] I got a 7800 question...please don't flame me :) From: "Eric Ball" <ericball@xxxxxxxxxxxx> Date: Tue, 22 Jul 2003 17:52:05 -0400 |
From: "Dennis Debro" <ddebro@xxxxxxxxxxxxx> > I was looking through the 7800 documentation and I see no mention of the stack. Where is it? $100 - $13F is documented as being a shadow of page 0 (TIA and MARIA) and $140 - $1FF seems to be used by the 6116 (RAM chip). Does the 7800 have a full page for the stack? A good question. The 7800 RAM memory map is full of weird shadows, but the following is all that is needed: 1800-203F 2K + 64 bytes 2040-20FF 192 bytes 0040-00FF ZP shadow 2100-213F 64 bytes 2140-21FF 192 bytes 0140-01FF SP shadow 2200-27FF 1.5K So there is 4K total, but two chunks are also used for zero page and stack memory. (Unlike the 2600, the two don't share RAM on the 7800.) It should be noted that the 6532 RIOT RAM is mapped to 0480-04FF but should not be used in 7800 mode. The 6502 runs 50% faster in 7800 mode, and MARIA has to slow it down for TIA and RIOT register accesses. > Also how do you check for collisions? Do you use the same methods used with the 2600? Yep, the same methods. Ohh, you mean the TIA collision registers :-) MARIA doesn't have any collision registers, so your game has to track sprite positions and handle and collisions manually. (The sprite list concept used by the 7800 doesn't lend itself to simple collision flags anyway.) ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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