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alex_79

Member Since 7 Sep 2006
OFFLINE Last Active Mar 9 2019 12:32 PM

#2787989 can reproduction carts be made as pal from ntsc

Posted by alex_79 on Sun Jul 7, 2013 10:06 AM

There isn't any difference hardware-wise between a PAL or NTSC cartridge. Only the code (the rom) is different.
So the only way to convert a NTSC game to PAL is to have a programmer to alter the code. This has already been done for a lot of games. There are some ready to download here, and you can find many other conversions in the "hacks" forum.


#2777278 Has there been a homebrew that uses the 4-ports of a Sears VA II?

Posted by alex_79 on Wed Jun 19, 2013 12:57 AM

Is there a way to use the extra ports for joysticks? Perhaps a programming trick?

Nope, there aren't additional input lines on the SVAII/2800, just the usual 10 digital inputs and 4 analogue ones with the only difference that, if you select paddle mode using the switch on the console, they are rearranged across the 4 ports to make use of the special controllers which have a different pinout (only one paddle line per controller and action button on a different pin)

The possibility to have more than two joystick on the 2600 was discussed in the forums and it's indeed possible but it requires external hardware.


#2774182 Atari 7800 arcade-style joysticks

Posted by alex_79 on Fri Jun 14, 2013 5:27 PM

I have this diagram that shows the 7800 joystick ciruit (I don't remember where I downloaded it from):
7800_Joystick_circuit.png
With the 7800 In single button mode (and on the 2600), pin 6 is read to detect a button press. Normally it is HIGH (because of the 10k pullup inside the console) and it goes LOW when any of the 2 button is pressed because it's connected to ground through the pulldown small resistors in the joystick. The paddle lines are always LOW in this situation. So both buttons on a 7800 controller act like the single 2600 button in this case.

When a 7800 game set the 2-button mode, there's a strong pullup active on pin 6 and the 2 buttons are read on paddle lines (pin 5 and 9 ) with inverted logic. Normally those pins are LOW (because of the 2 pulldown resistors), while by pressing a button the corresponding paddle line goes HIGH because it gets connecetd to pin 6. 2-button mode is disabled in a 7800 console if the TIA video out is enabled (that is in 2600 mode) and that part of the circuit is not present in a 2600 console. Without the resitors the paddle lines would always be LOW (and no button could be read) and the output of the transistor Q6 would be shorted to ground when a button is pressed.

The reason for this complicated scheme was to have both buttons working also with the old 2600 games. Consider that the prolines (and later the joypads) were packed with the 2600 junior console in Europe and it wouldn't have looked right to have one button non funcional.


#2647648 CD4050 A/V mod on PAL atari 2600

Posted by alex_79 on Wed Nov 28, 2012 12:22 PM

I connected all pins of the TIA to the original Atari board, exept the Lum0 - Lum1 - Lum2 - Color -Sync - Audio pins.

Those pins require pullup resistors (R29, R30, R31, R33, R34 and R35 in the PAL jr schematics): if the TIA isn't connected to those on the Atari, you'll have to add them on the external board.
schem.jpg


#2635310 Birthday Mania - Unwrapped

Posted by alex_79 on Thu Nov 8, 2012 2:44 AM

Nice work, Waggie! The source code could be a nice add on for the package, maybe printed on a continuous perforated paper with a dot matrix printer, to make it more authentic...
If I understand correctly you don't have the rom, but you have to reconstruct it from the printed code, right? At least it will be easier to implement the code to personalize the name, and you could easily convert the rom in PAL or PAL60 format if you want to.

Recreating the label won't be a problem as the artwork is very simple. This is what I came up with after tinkering a bit with Gimp and Inkscape using the two known (blurry) pictures as reference.
bm_cart.jpg
I'm sure that some of the talented artists here on AA can do a much better job. If the labels are printed to order you could also have someone create a tool to have them personalized with the name of the owner, instead of writing it afterwards.


#2625747 TIA programming guide by COLECO

Posted by alex_79 on Thu Oct 25, 2012 6:56 AM

I found a scan of a VCS programming guide from Coleco. I 'collect' all the tech docs about the VCS that I can find on the web and while I had quite a few versions of the "Stella Programmer's Guide" from Atari I never saw this one before. The file can be found on "The ADAM Resource" website in the technical manuals section. The doc is called "Coleco TIA.pdf", it lacks a few pages which are on another file "Coleco TIA Schematic.pdf" on the same web page. I haven't read it entirely yet, so I could be wrong, but I think the only reference to Coleco is in the filename. TIA is referred to as VIC (Video Interface Circuit)

It seems to me more detailed than the Stella Guide in describing the VCS workings (it also include code snippets in asm), so it might be useful for someone learning VCS programming. The only drawback is that it uses different names for the TIA registers and graphical objects than the 'standard' ones. Here's a corrispondence table:



Object A,B -> Player 0,1
Projectile A,B -> Missile 0,1
Border -> Ball
Foreground -> Playfield

TIA registers:

VBLNK = VBLANK
HSYNC = WSYNC
CRHOR = RSYNC
OBASR = NUSIZ0
OBBSR = NUSIZ1
CLROA = COLUP0
CLROB = COLUP1
CLRFB = COLUPF
CLRBG = COLUBK
BDRSZ = CTRLPF
OBADR = REFP0
OBBDR = REFP1
FGNDA = PF0
FGNDB = PF1
FGNDC = PF2
CROBA = RESP0
CROBB = RESP1
CRPJA = RESM0
CRPJB = RESM1
CRBDR = RESBL
SNDAS = AUDC0
SNDBS = AUDC1
FREQA = AUDF0
FREQB = AUDF1
LVLSA = AUDV0
LVLSB = AUDV1
OBJAF = GRP0
OBJBF = GRP1
PJAEB = ENAM0
PJBEB = ENAM1
BDREB = ENABL
HMOBA = HMP0
HMOBB = HMP1
HMPJA = HMM0
HMPJB = HMM1
HMBDR = HMBL
OBARS = VDELP0
OBBRS = VDELP1
BDRES = VDELBL
PJATK = RESMP0
PJBTK = RESMP1
HMENB = HMOVE
HMRST = HMCLR
OCRST = CXCLR


I integrated the pages from the two PDFs into a single document in the correct order and also rotated those with diagrams in landscape orientation to make it easier to read on a PC monitor.
I always prefer the DJVU format for scanned documents as it results in smaller file size and the viewer software is lightweight and fast even on old pc, so I converted the document in this format. I added OCR text as well so it is now searchable.

Here is the link of the fixed file, I also included a PDF version, but it lacks the OCRed text.

DJVU
PDF


#2609455 Having Atari trouble!

Posted by alex_79 on Sun Sep 30, 2012 2:18 PM

Have you pressed the RESET switch on the console to start the game? Older games cannot be started by pressing the joystick button.


#2608732 Convert Atari 2600 Jr (Long Rainbow) Pal to NTSC

Posted by alex_79 on Sat Sep 29, 2012 3:09 AM

The 2600 doesn't have any region lock system, so it will run games of any format, anyway the palette is different between PAL and NTSC TIA chips, and the frame rate is deternmined by the game program. So if you mix games and console with different formats you will have a TV signal with the color encoded according to the format of the console but with number of scanlines and framerate according to the format of the cartridge. Even if your TV accept that non-standard TV signal (PAL TVs usually displays a 60Hz signal without problems), the colors in the game will be incorrect because of the different palettes and there's no way to correct that.

This only applies to the 2600, other consoles may behave differently: usually the frame rate is not determined by the game, but by the graphic chip in the console and sometimes it can be selected by changing the signal on one of the pins (you can install a 50/60Hz switch in that case) and the palette might be the same or very similar between different formats.


#2600499 SHIPPED: Atari 2600 Red Sea Crossing

Posted by alex_79 on Sat Sep 15, 2012 2:31 PM

If I would buy it I'd like the artwork being like the original but without the flaws of the cheap printing process used at the time. A small variation of the copyright line and a nice glossy label with today standards printing quality will make it easily recognizable as a repro, while still being quite true to the original.

Something like this
rsc.jpg


#2541396 Finally Got Around to Making One of These...

Posted by alex_79 on Thu Jun 14, 2012 10:01 AM

However, people "could" hack the games to be compatible with the 2nd button of a 7800 controller instead. The reason they haven't been (as far as I know) is because Genesis controllers are much more popular & abundant than 7800 controllers. Maybe we should request that when someone make a 2-button hack, they make a 7800 controller version as well. edit: I think this was mentioned before and there may have been more reasons behind not doing it. I don't remember.

The 7800 controller is wired so that both buttons are normally seen by the console as the standard 2600 single fire button. In order to distinguish between the two, one of the pins on the controller port inside the console must be be pulled high. The 2600 doesn't have the circuitry to accomplish that and the 7800 is designed so that it can be enabled only in 7800 mode.
So no 2600 game can use the two independent buttons of a 7800 controller, no matter which console the game is running on.


#2536456 Stella 3.7 released

Posted by alex_79 on Tue Jun 5, 2012 3:56 PM

Thanks again for the hard work, Stephen. I played a bit with the new TV effects and they're great!

The garbage data generated by irregular scanline counts is now fixed. If the display tries to generate too many scanlines, the entire screen is blanked. And if the current frame has less scanlines than the previous one, the excess scanlines are blanked. This will be present in 3.7.1.

I think that in case of too many scanlines it would be more accurate to "roll" the screen, i.e. start a new frame after the max number of scanlines. This allows to display correctly the cycling color screen in "Video Chess" while the computer opponent is "thinking", for example. In that case the program doesn't strobe VSYNC nor VBLANK and the screen actally rolls, although it's not noticeable, because it's entirely filled with a solid color.


#2534749 Hooking up my atari to my "new" old tv

Posted by alex_79 on Sun Jun 3, 2012 4:27 AM

Well... Not really an issue with the contrast/brightness. First nothing but snow appeared on the screen. Now I scanned for channels I put the atari2600 on channel 2

That's because "channel" here refers to the television channel frequencies defined in the TV system used in the country where the console was sold.

AFAIK, for TV set sold in US, the channel numbering always matched channels defined in US TV system, so a channel scan wasn't needed when buying a new TV (pressing channel 2 on the remote actually tune the TV on the frequency defined for channel VHF 2).
This was not true in Europe, where tipically each "number" on the remote was just a preset that could be programmed to tune any channel. So you must always do a frequency scan to use an equipment which outputs an rf signal on PAL TV; then you can store that frequency on any channel preset on the TV.

Atari 2600 PAL-B (sold in continental Europe) used channel VHF 3 or 4 (although on the case was stamped channel 2-3, because they didn't modified the mold), while PAL-I units (for UK and Ireland) used channel UHF 36 and they didn't have a channel select switch.
Note that channel frequencies are not the same in different TV system. For example I live in Italy, where system B/G was used (B for VHF and G for UHF). To use a atari 2600 from UK (PAL-I) on my TV I had to tune an inductor inside the console, because channel UHF 36 in system I is different than channel UHF 36 on system G (The main difference in this case is the audio carrier frequency, so I only got the picture without audio before tuning the console).


#2439795 Mirrored memory

Posted by alex_79 on Sun Jan 8, 2012 6:17 AM

  • Does a change in one location make a change in all the mirror locations (including the original if you change a mirror value)?
  • Is only one location active at a time, or is the original and all its mirrors active at the same time?

There's only one physical location which responds to different addresses because the value of some of the address bits is ignored. So changes affect all mirrors.
I use these documents (by Chris Wilkson) as reference for the 2600 memory map:
Attached File  mem_map_1.txt   27.36KB   403 downloads
Attached File  mem_map_2.txt   1.75KB   271 downloads
Attached File  riot_map.txt   6.05KB   269 downloads
Attached File  tia_map.txt   3.56KB   281 downloads


#2391914 Pros and cons of a 7800 over a 2600

Posted by alex_79 on Wed Oct 19, 2011 10:45 AM

Cons, no wood

:-D
pb230023.jpg


#2355647 Tips for repairing select/reset buttons of Atari 2600 Jr?

Posted by alex_79 on Tue Aug 23, 2011 11:39 AM

There's a flex mylar circuit under the switches that connects to the motherboard. You can try to clean it, but if the traces are worn out you'll need a replacement.
A much simple solution, if you don't mind about originality, is to install two pushbuttons somewhere on the case and solder wires directly on the board.
You can see a couple examples in this thread.