What is happening here?

Mike · Post by **Mike** » Tue Dec 11, 2012 3:04 pm

Hi!

First of all, thank you for your responses. They gave me hope I was not totally off track with this project.

So, where is it at?

@Jeff-20 and @Witzo: It is in order to be conscious about whether one wants to keep the purist approach and/or is cautious to keep working hardware working ('if it ain't broke - don't fix it') ... I simply had this dream about what could be done on the VIC-20 with just a little bit 'nudge', and I am happy you appreciate the result!

@Boray: I could quite as well ask why people still want to program on the VIC-20 for that matter.

The mod can also be used for other things, like double-buffering (parts of) a bitmap. Also, you are not confined to still images, there is still some CPU time left while a full format VFLI image is being displayed.

@joshuadenmark, @crock and @darkatx: I understand it is not an easy decision to undertake the mod - even when one is good at electronics and soldering -, when there is only one VIC-20 to tinker around with. But if you come to do it, welcome to the club!

@ral-clan and @RobertBe: The hardware mod can also be done on a NTSC VIC-20. However, at the moment there is actually no display routine available for V(I)FLI images. Target resolution would be 168x384i in 16 colours.

Half a year ago, Eslapion donated a defective NTSC VIC-20 to tokra, who in turn sent it to me. In the last days, I found the time to repair it, and while being at it, implemented the first part of the mod as well. Incidentally, it is also a 2-prong VIC-20. The other two combinations, PAL 2-prong and NTSC DIN are equally possible. Expect results at the beginning of next year - here is a view of the 'proof of concept' work:

The adapter sockets with the free wiring will be replaced by a PCB carrying just the 8K RAM chip and a few SMD parts.

Muzz73 · Post by **Muzz73** » Tue Dec 11, 2012 4:36 pm

I, personally do not have the technical ability to do this, but would love to see it in action.

16KVIC20 · Post by **16KVIC20** » Tue Dec 11, 2012 5:08 pm

I couldn't do the mod myself, and having just one VIC 20, I'd be reluctant to have it done anyway. I think it is an interesting project though; it's always good to see the VIC stretched beyond its normal abilities.
It's a shame a cartridge version could not be available, but I suppose that is technically impossible.

PaulQ · Post by **PaulQ** » Tue Dec 11, 2012 6:10 pm

Hey, Mike. I saw your post too. Excellent work. I have two Vic 20's, one has a bad video chip. I considered duplicating your efforts, but then I felt as Boray did. I like to program the Vic because its inherent limitations acts as a creative lens. Don't be dissuaded by this opinion; take it as this modification being your unique thing to show off what you can do to the world. Your uniqueness adds to the diversity of this community, and I think that's needed.

What would be really cool is if someone were able to replicate video chips to restore otherwise dead VIC's.

rhurst · Post by **rhurst** » Tue Dec 11, 2012 8:08 pm

Yes, I echo a lot of what PaulQ just said, it gets no plainer than that... you give a lot to this user community that thrives from unique talents such as yours. And it is a good reminder to us all to reflect appreciation to such creative efforts.

Like most others, way beyond my skill... and while I can still dream of being that technically skilled at modding, heh, I'd be butchering too many good VICs in my possession if I try. And if I were successful, well, I'd probably be left wanting more. What else ya got??

RobertBe · Post by **RobertBe** » Tue Dec 11, 2012 11:15 pm

Mike wrote:The hardware mod can also be done on a NTSC VIC-20. However, at the moment there is actually no display routine available for V(I)FLI images. Target resolution would be 168x384i in 16 colours.

Without a display routine, there would be no purpose to mod a NTSC VIC-20.

The adapter sockets with the free wiring will be replaced by a PCB carrying just the 8K RAM chip and a few SMD parts.

Ah, that would be much neater.

Simple is good,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug

matsondawson · Post by **matsondawson** » Wed Dec 12, 2012 2:41 am

Would it be possible to add an adapter to the cart port that exposes the VIA bus on via cycles for RAM1,2,3? I'm guessing you'd have to decode the RAM1,2,3 for the VIA cycles, and block any chips selects/RW coming from the CPU. Maybe about 5 ics worth?

Edit:
Wouldn't require any soldering then.
Of course that wouldn't give you all that extra colour ram... or would it?

ral-clan · Post by **ral-clan** » Wed Dec 12, 2012 8:50 am

Occasionally I will view these amazing new VIC images on the internet and marvel....so your work is certainly appreciated, even if I haven't implemented it at the moment.

Mike · Post by **Mike** » Wed Dec 12, 2012 9:09 am

@Muzz73: In the corresponding thread in the Hardware section I posted some photos, where VFLI images are on display on a monitor. The newer posts feature examples which were rescaled from the test output of the converter to match the pixel aspect ratio correctly.

@16KVIC20 and @matsondawson: The RAM data and address lines which are directly connected to the VIC chip are not exposed to the cartridge port. There are three 8-bit buffers acting as timing barrier inbetween. These buffers separate CPU bus and VIC bus during VIC fetches. The colour RAM even gets separated from the normal (VIC) data bus with yet another analogue switch during that time.

When you want to make the 3K extra RAM accessible to the VIC chip, you must add it at the correct side of the buffers, and that is only possible on the mainboard.

@PaulQ and @rhurst: I also hope that others always remember that everyone here in Denial can contribute to the community.

@RobertBe: While the mod might also serve other uses (like expanding to a contiguous 30.5 K BASIC memory, i.e. 31231 bytes free), you see there's an NTSC 6560 depicted in the photo - a corresponding display routine is in the works.

@ral-clan: That being said, you surely can imagine the anticipation, when the new display system was fired up the first time and hardware and software worked right together on the first try.

matsondawson · Post by **matsondawson** » Wed Dec 12, 2012 3:22 pm

> When you want to make the 3K extra RAM accessible to the VIC chip, you must add it at the correct side of the buffers, and that is only possible on the mainboard.

The plan was to have an adapter you plug on the main board that also adapts to the cart slot. i.e. you plug onto the VIC side of the bus and the cart slot. You'd still have to open your machine, but you wouldn't have to solder it.

Mike · Post by **Mike** » Wed Dec 12, 2012 4:15 pm

The internal RAM expansion does not only have to add connections (which could easily be done with some plug-in board contacting chip pins from above, or similar), it also needs to break connections on the mainboard.

My variant does this without the need to cut traces on the mainboard itself, rather the relevant chips are put into sockets - and where a connection has to be rerouted, the relevant pin of the chip is bent straight beforehand, and the connection is rewired.

TLovskog's variant does not replace the original chip select logic and RAMs, rather there's a PCB which plugs into the character ROM. Not all VIC-20's have this chip socketed, and it also requires to break traces on the mainboard and solder wires to other chip pins, so it's no better off.

As I wrote earlier, CPU bus and VIC bus are separated during VIC fetches. This is necessary, because the 6502 can't tri-state its address bus. When the bus buffers are enabled, the 6502 selects the direction of the data bus buffer over its CR/W line, and the address bus buffers are fixed in the direction CA -> VA. Even though the /RAMx signal lines actually reflect VIC fetches in the range $0400 .. $0FFF, that doesn't buy you much, the complete VIC address never reaches the cartridge port.

In my variant I especially took care, that the (now open) original /RAMx signals on the mainboard are tied to H-level. This is necessary for reliable operation of UD9 (which decides, whether CPU bus and VIC bus are to be separated) and to reliably disable external RAM expansions in that range. Otherwise, the open inputs of UD9 put a signal level of around 2.4 volts on the /RAMx lines, which is undefined for CMOS inputs!

I don't see any solution which implements this mod without some soldering work on the mainboard.

Vic20-Ian · Post by **Vic20-Ian** » Thu Dec 13, 2012 6:26 am

Mike,

from my point of view this is a variation of inventor not understanding the market problem.

You have invented something and think it is wonderful. It solves all your display problems or needs etc.

I don't have the same problem or need therefore while I can appreciate it as a technical achievement, it has no commercial value to me.

By commercial value I mean I see no need to invest my time or any money in doing this as I would not use my Vic-20 to do this, much as I enjoyed seeing the demo pictures and was amazed.

I use my Vic-20 as a Vic-20, to play games and a bit of programming with it's delightful standard resolution.

I love my Simple, Friendly, Low resolution Vic-20 as it is and much more than I could love an internally hardware modified, Franken Vic.

This may seem at odds with my support for the Final Expansion 3. I use this as a multi rampack and for quick fix on favourite games really it is overkill for what I need but it is convenient to have the Ram and the SD2iec drive.

I appreciate your work and congratulate you but I just don't want to buy into it myself.

Keep going, don't stop just because we don't want to do it.

PaulQ · Post by **PaulQ** » Thu Dec 13, 2012 5:25 pm

Mike wrote:@PaulQ and @rhurst: I also hope that others always remember that everyone here in Denial can contribute to the community.

The simple expenses of money, time, and space it takes to acquire, maintain, and occasionally use a working Vic 20 computer in 2012 represents a contribution that most people would be unwilling to make.

rhurst · Post by **rhurst** » Thu Dec 13, 2012 9:16 pm

... that most people ...

Meaning "regular" people, not us freaking geeks!

ral-clan · Post by **ral-clan** » Fri Dec 14, 2012 7:34 pm

Mike,

You should consider doing a write-up about your new graphics mode and hardware modifications for Commodore Free magazine. A lot of people (more than on Denial, anyway) would read about it, be impressed by the images and perhaps try it.

Commodore Free magazine is always looking for articles, and your graphics mode would be a "meatier" and more significant article than they many reviews of old games that are often needed fill that magazine.

http://www.commodorefree.com/