DanBoris

The trick to conquering the 7800's graphics system is to think of it as a 2 step process. Instead of going directly from game logic to the data structures, you can have an another layer of code in between, a display engine. The display engine could, for example, take a table that contains the sprite postions and what "character" to use for each sprite, and convert this into the data structures that the Maria graphics chip uses. Now you game logic writes to the table, and then you call the graphics engine once per frame to setup the data structures. The cool thing about this is that it allows you to write display engines that mimic almost any type of graphics hardware. Dan

As a last resort you may want to open up the cartridges and clean them again. You will find that you can do a much more thorough cleaning when the circuit board is out of the case. Dan

The EPROMS and EPROM cart are not uncommon. These were made by people as a way to pirate games. Not sure what you mean by a ROM scanner? Dan

Try Best Electronics: http://www.best-electronics-ca.com/ or B&C ComputerVisions: http://www.myatari.com/ Dan

Sounds a bit like Gauntlet (not to be confused with the Atari arcade game). You can see a picture here: http://oldclassics.narod.ru/atari/atarig.html Dan

You should also try cleaning the cartridge slot. Dan

The Antic doc can be found on Atari-History.com in the Document Library. I have the 5200 article on my web site http://atarihq.com/danb

Vertical scrolling is much easier. To scroll vertically you just change the pointer to the start of video memory in the display list. This will give you course vertical scrolling, and you can use this along with the VSCROL register to do fine scrolling. With horizontal scrolling you have to setup each mode line in the display list to load a new memory pointer, then change all these addresses to scroll the screen. Horizontal also requires a slightly more complex layout of you video memory. Dan

I've been scanning in the copy of the 7800 Software Guide that I have and converting it to text to keep the size down. Hope to have it available on my page in a couple days. Dan

The other problem with porting 8-Bit Basic games to the 5200 is that a lot of basic programs relied on functions of the BIOS in the 8-bit which you don't have in the 5200. Dan

On difference is that the NES 6502 doesn't support the decimal math mode which is useful for scorring and such. Yes, the Maria chip handeled all the movement of graphics data from memory to the display, but when these DMA transfers where happening the CPU couldn't do anything so the DMA did cut into the usable processor cycles. Not sure if this is also the case for the NES. The TIA chip did handle the controllers and sound, but it was just an IO chip so the processor still had to do all the work. Also to make matters worse the cpu clock slowed to 1.19Mhz when the TIA is accessed. The NES used a 6502 processor which can only access 64K of address space, so 128K would be impossible without bankswitching. From a quick look at the NES tech docs it appears that it had a 32K address space for cartridges as compared to 48K on the 7800. The physical size of the NES carts was probably an advange since they had a lot of room to put more ROM chips. Actually a number of the 7800 carts included extra RAM. It's hard to compare the graphics systems on the two machines since they are radically different. The greatest strength of the 7800's graphics was it's incredible flexibility. For example where the NES sprites where either 8x8 or 8x16 pixels the 7800's could be almost any size. This flexiblity was probably also one of the 7800's biggest liabilities since it made programming the system a lot harder the programming the NES. You really had to create your own display engine for each game. For example if you wanted to have a table in RAM with the positions of your sprites and a pointer to the graphic to use for each one, you would have to write code that read this table, and then setup the data structures that the Maria used to draw the screen. Made programming more difficult, but gave you incredible flexibility. Dan

I don't think the arcade industry tanked as quickly as the home game industry. Check out this thread: http://www.atariage.com/forums/viewtopic.php?t=15837 I did a graph that shows the number of new arcade games released each year, and you can see the the numbers leveled off after 1984, but they didn't start a sharp decline until the end of the 80's. I distinctly remeber arcade still going strong in my area for a few years after the crash. Arcades used to be great because the technology of arcade games was so far beyond what you could get at home. Today with the power of home systems the only major things arcade have to offer from a technology standpoint are the big "interactive" type games, like the skiing, snowboard, jetski simulators, etc. I imagine that the cost of these machines makes it hard to make a profit from them. I think one of the big factors contributing to the crash was the incredible speed at which the industry grew. It's hard for any industry to sustain that kind of growth and remain stable. Dan

My F18 Hornet has it also. It's a 1.5K resistor connected from +5 to the clock line, must be a pull up resistor, although I don't know why it's necessary. Dan

I have some information and tools on my site http://atarihq.com/danb. Also check the links on my site to the Atari Historical Society, there you can find the "3600 software guide" which gives you a lot of information on programming the 7800. Dan

It would not be an easy conversion since the 7800 uses a radically different video system from the 5200, so all the video code would have to be re-written. Also the controllers are different, and the sound chip is different, so you would basically have to re-write everything but the game logic. Dan

Videtopia was an excellent traveling video game exhibit http://www.videotopia.com/ They haven't been any place in over two years, so I don't know what thier current status is. Dan

I've been digging through a disassembly of the ROMs you posted on your site for these, and discovered that like the 850 interface module, these units did have driver code built in that got downloaded to the computer. I even found the code that does the download, but I can't find where this code is called, so it's possible it doesn't work. I'm having fun trying to figure out how these things worked! Dan

I think it only appears on carts that have something more then the standard 32K ROM, either more ROM, extra RAM, or a POKEY. There are a lot of games that have these features that don't have the Super Game label, but I haven't seen any cart that has the label and is a standard 32K cart. Dan

The abbreviation "TYP" for Typical, is common on schematics. It is used to indicate a section of a circuit that is duplicated multiple times, but only shown on the schematics once. Dan

Joysticks: Each pot input has an RC network (resistor/capacitor). There are two capacitors on each input. As you noted the schematic only shows two, but each one is labeled "TYP-8", meaning that the capacitor is repeated 8 times, once for each pot input. Each controller has two 640K pots which connect to the pot inputs, and also to an adjustible pot centering circuit. Keypad: The scanning circuit in the Pokey chip is switched to a specific port under software control, so if you are only connected to port 1 there is no way to see which of the other ports is being scanned. Dan

You can also get a version that runs in DOS/Windows on my page: http://atarihq.com/danb/a7800.shtml Dan

The are similar 3-digit numbers imprinted on the bottom of 2600 system cases near the power jack. One possibility is that these identify the person who did the final QC on the unit/cartridge, although 999 numbers doesn't seem to be enough for this. Dan

The situation with ET was the amount of time they had to develop it. I was written in 6 to 8 weeks , and incredibly short time for a 2600 game. The time was so short because Atari wanted it in the store for Christmas. Dan

I always liked Starfire, used to play it a lot back in the day. I had never seen a stand up version of it, I only rember the sit down. Exidy actually was still in business as of a year or two ago, but has since gone out of business. Dan

I actually built one of these back in the day, worked pretty good. I think I still have it around somewhere. Dan