Does anyone know if Gun Fight have free play?
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Going by the dipswitch doco the answer is no.
Does anyone know if Gun Fight have free play?
Any idea if i can wire the Credit switch to the coin credit?
The 1975 B&W game?
It has about half as much 8080 code as Space Invaders; less than 4kB total. Shouldn't be too hard to find the code and hack in a freeplay. Figure that's maybe 20% data or blank, and estimate about 2 bytes per line of code on average... so I'd guess it only has maybe 1600 lines of code.
A bigger problem might be burning new EPROMs. I think that has 2708s... or some sort of 1kB device.
Sweet! But to be sure is this from the mame set? (IE intended for 2708?)
And if you don't mind sharing, can you tell me what two bytes were changed? (so I can keep a note incase I ever need to mod another image?)
Well, I was sitting down, relaxing this evening, and found I had some time to kill when I saw this post... at 6:35PM. (EDT).
The hack was done and tested at 6:53. 18 minutes to do it, including playing a couple of games. Exactly two bytes were edited. Mind you, this is a very simplistic (dumb, even) hack. It's not dipswitch selectable (always freeplay). It doesn't say "freeplay" or anything (still says "insert coin" in fact). But if you press start, even with no credits, it starts a game.
Enjoy.
Nice work. Now you should try this on Sea Wolf.
Yes, file is from the MAME ROM set. I don't have a Gun Fight, so MAME is all I can do. It's a 1K file... I guess it's a 2708 on the PCB, but may be some other old-ass 1K PROM. I assume it's possible to combine the images and re-strab the PCB for 2716s, but again I don't have the hardware to verify.
Bytes changed (offsets into the subject ROM): 0x176 from C8 to 00, 0x177 from 3D to 00. This could be easily seen using the DOS command FC. "FC /B file1 file2" will do a binary compare and report the differences byte by byte.
The first byte changes a "rz" opcode, that originally would return if the credit count is zero, to a "nop", so execution proceeds even if there are zero credits. The 2nd changes a decrement opcode to another "nop". The decrement originally reduced the credit count by 1. But we don't want to do that if there are 0 credits, as it would leave us with 255 credits.
A side-effect of this hack I noticed while playing some more is that if you DO coin it up (so that there is no longer 0 credits), it'll keep re-starting ("HEY PARDNER! YOU'VE GOT CREDIT!") for ever (because the code to decrement the credits is gone). Well, not forever, just until you power cycle it. So... with this freeplay hack, don't insert a credit! (shouldn't be a problem... that's why people want freeplay hacks, so they don't have to insert coins)
As a bonus, if you want to burn another ROM, here's a hack to change "INSERT COIN" to "FREE PLAY" at the bottom of the screen.
So since the freeplay ROM requires you to press the "START" button to begin a game (whereas the original started automatically when it was coined up), I decided to take a look as the start button. I googled and found a pic of the control panel... and there was no start button(!) Searched a little more... aparently these had a coin door with a start-button built in (kinda like a pinball coin door). Wacky.
Mame rom set is basically for 2708's, but pretty much all the GF boardsets I've worked on so far have been 3604's or 7641's, which since there's 8 I'm assuming are along the lines of 3604's.
The mame set doesn't match what the 3609 set has either - 3 bytes are different, but I haven't had the time or motivation to figure out why they're different (yet).
Ironically I'm working on Gunfight rom issues tonight, so if I have an extra 2716 I'll fry one up and let you know if/how it works![]()
I just gotta figure out how these are put into 2716s now and to what location on pcb. I have two pcbs I'm tracking down issues on and think both are bad roms.