lance.ewing wrote:Any ideas what Data Catalog this 6562 document came from? http://archive.6502.org/datasheets/mos_ ... 63_vic.pdf
It is a different version than what is in the 1981 Component Data Catalog for the 6562, which contains a much fuller version.
Yeah, I'm aware of that. I was thinking of doing exactly that if I ever happen to attempt building an Attack UFO clone in hardware using the VIC 20 version of the 6560. The problem is that the game is putting a 1 in the colour RAM bit 3 for at least two of the colours used on the screen. If it is doing that for specific characters on screen, then it is highly likely that that colour data line is wired up in the original Attack UFO machine. The screenshots of the MAME emulation suggest that there are two different shades of blue, i.e. the darker blue of one set of UFOs and lighter blue of the barriers at the bottom. Those lighter blue barriers are using one of the colours where there is a 1 in bit 3 of the colour RAM.
My assumption is that the ROM images available online are the unmodified ROM data. There is no reason I can think of for the MAME team to have modified the ROMs. Isn't it their goal to build an emulator to run the unmodified ROMs? It's the code of their emulator that they change to make it run a new set of game ROMs, usually by building a driver that specifies what chips are used by that machine. In the case of Attack UFO, they had to alter their 6560 chip emulation so that it didn't support multi colour mode or the reverse mode when running Attack UFO. If altering the ROMs was an option for them, then they wouldn't have needed to add Attack UFO specific customisations to their 6560 emulation. So I think those would be the original ROMs.
Never looked at the 6562 before, but from the spec it looks like they simply doubled the pixel clock, changed the horizontal counter and left most of the remaining part to itself. From a development point of view, I would think that the 6560 was finished by the time they started on it.
I was under the impression that the ROM had been fiddled with, but you may be right that its only the MAME part that has been changed. Who knows.