DanBoris

This isn't ans big a problem on the 7800 as on the 2600. On the 2600 the bankswitching was done entirely inside the ROM chips, so if you wanted to do your own bankswithcing you had to do it yourself. The 7800 on the other hand used standard ROM chips in all carts, and bankswitching was implemented with standard logic IC's inside the cart. So if you can get a pile of common bankswitched 7800 carts you can just replace the ROM with an EPROM and you have bankswitch cart. Dan

This might be a stupid question, but are you sure your Joystick is ok? Dan

Ok, I think I got this figured out. It jurry-rigged a cable to connect an 800XL so I could test things out easily and I think I found the missing piece of the trackball puzzle. The key is bit 2 or the CONSOL ($C01F) register which enables/disables the pots in the controllers (I believe a 0 disables the POTs). When you disable the pots in a normal controller they always return $E4 which is the max pot value that can be returned. But when you disabled the trackball it returns a $7A which is also the value that the trackball returns when it is at rest. So you can use this to determine whether a trackball or stick is connected. As for the trackball range I found that it ranges from $A6 to $57 with $7A being the centred value. Dan

Yes, the Lynx did use a 6502 along with the 2600 (6507 variant), 5200, 7800, and all the 8-bit computers. Dan

What system are we talking about? As a general note to anyone who posts a programming question, please indicate (preferably in the subject line) which system you are talking about. I've read more then one message here where it took me a while to figure out what system was being discussed. Dan

I was just playing Hex the other day on one of the ST emulators. It was an excellent game, sort of a thinking version of Q-Bert. Dan

Maybe they used the speaker originally because they felt it sounded better for the clicks to be coming from the keyboard then from the TV. Well it's really a trade-off. If they where horizontally positionable then they would have to had a limited height, say 8 or 16 lines. This would have reduced thier flexibility. Having the sprite the full height of the screen makes vertically muxing the sprites very easy, since at the start of each frame you can draw the appropriate images into the correct sections of the PM memory, then just change the horizontal positon of the sprite on the correct scan line. Dan PS: I find the subject of the trade offs made in hardware design a very interesting topic of discussion.

This was probably done to cut the manufacturing cost of the system. Wouldn't have saved a lot itself, but combined with a lot over other simplifictions between the 800 and XL line they probably brought the manufactuing costs down quite a bit. Remeber that the GTIA in the computers was a direct descendant of the TIA in the 2600. The disaply data on the 2600 was generated on the fly one line at a time, so it had no concept of vertical positions, thus no vertical position registers. The 2600 also had no directly controllable horizontal position registers, so at least we gained that in the GTIA Dan

Although this is true, the real cause of the problems you mention is just poor programming. The flicker is something that would have been known about when the game was developed so the game software should have been written to compensate for it with respect to collision detection. So the authors either didn't notice these glitches or just chose to ignore them. Dan

Credit where credit is due, I am still the original author of O2EM. Andre de la Rocha has been kind enough to do some updates recently and I have been releasing the new versions for him. Dan

This sort thing was not really that unusual, devices like this where made by a couple different companies. I have one that holds 6 carts and has a button in front of each slot to select the game. Dan

The information in the Stella doc is about as detailed as you will get. You will not find anything that documents every details of the TIA all in one place. The best bet is to start with the Stella doc and try to get Combat working based on that. Combat doesn't do anything tricky so it's the easiest to get working. Then you will have to start modifying your emulation to support all the tricks that other games pulls like mid-line changes etc. Dan

O2EM is the only O2 emulator out there. Get it at http://atarihq.com/danb Dan

According to Kevin Horton's guide to 2600 bankswitching: http://www.tripoint.org/kevtris/files/sizes.txt the Megaboy cart is the biggest at 64K and Fatal Run is 2nd biggest at 32K. This of course doesn't include the supercharger games which loaded different sections from tape. Dan

Best Electronics http://www.best-electronics-ca.com/ sells them new in teh box $69.96. Dan

Check out Amazon.com there are still a couple 68000 programming book in print. Also Best Electronics http://www.best-electronics-ca.com/ also sells a couple 68000 programming books geared towards the Atari ST. Dan

It's highly unlikely that the 6507 would work at all at that speed. The fastest full 6502's back in the day only ran at a max ot 4Mhz, and I bet the 6507 was rated slower then that, probably 2Mhz. At best the chip wouldn't function properly, at worst you would burn it up. Dan

Ok, here is some advice from someone who has worked on a 2600 emulator... First be sure you have read an understand all the Stella documenation you can find, specifically the Stella programmers manual. You can get links to most of this at my site http://atarihq.com/danb Next, it sounds like you wrote your own CPU core, if so be sure you are counting cycles absolutly correctly. Be sure each instruction has the right cycle count and that you implement the instructions that have variable cycle counts the correct way. When you are emulating the TIA you have to do it on a cycle by cycle basis. You need to keep track of exactly where your "virtual electron beam" is on the screen so that any write to the TIA registers can take effect immediatly. You also need to know when during a scan line things happen. For example, when you write to the playfield register, at what point does this effect the display. This information is not really documented anywhere that I know of. You may be able to find information in the Stella Programmers Mailling List archive, there is a link on my site to it. If you need anymore info, please feel free to ask. Dan

Bounty Bob works like this: 4000-4FFF: ROM #1, 16K bankswitched in 4K sections. (use 4ff6-4ff9 to access) 5000-5FFF: ROM #2, 16K bankswitched in 4K sections. (use 5ff6-5ff9 to access) A000-BFFF: ROM #3, 8K non-bankswitched any accesses (read or write) to the the ranges 4ff6-4ff9 or 5ff6 - 5ff9 will cause the bankswitch. The logic for this shouldn't be too hard to implement, and since the 5200 carts are so large there is plenty of room for the extra logic chips. Dan

Do you have one of those TV's that switched to a blue screen when it doesn't get a signal? If this is the case then it's likely that you are not actually getting a signel from the 5200 to the TV. Dan

There are a couple major differences between the 5200 and 400/800 hardware. 1. The biggest difference is the controllers. The 5200 has no keyboard, but instead reads the keypads on the controllers through the keyboard input. The 5200 also doesn't have digitial sticks, the 5200 sticks are read like paddles on the 400/800. So controller routines would have to be re-written to port from one to the other. 2. The 5200 has not have a BIOS like the 400/800 (it has a small one but it doesn't provide you much). So if a 400/800 games uses a BIOS call it would have to be re-written. 3. The ROM, RAM, GTIA, and POKEY are at different addresses ranges on each system, so these would have to be resolved. So to do a port in either direction you would have to disassemble the game, make any necessary changes to accomodate the above issues, then re-assemble it for the other system. Dan

On a normal 5200 joystick the further you push the stick in a specific direction the higher (or lower) the value that you read from the sport. The trackball on the other hand is based on speed. The faster you rotate the ball the higher (or lower) the value that you read from the port. Dan

The next release of MESS will support Double Dragon and a bunch of other improvements to the 7800 driver as well. Dan

Yes, Steven Kent's book is also a very good one. Some people may have read it under the title "The First Quarter". .. and since we are recommending books, I've been reading High Score, The Illustrated History of Electronic Games by Rusel Demaria and Johnny Wilson. This is another great book that focuses heavily on computer games which is an area that doesn't get a lot of coverage in other video game books I have read. Dan

Sounds like the Amiga Power Stick, you can see picture here: http://www.cedmagic.com/tech-info/remote-c...ower-stick.html Dan