which chip for a video adapter

[vespacla]

Hello everybody !! I'm new to this forum !!

I'm currently building a rather simple 6502 based-homebrew computer. I luckyly found some very interesting information on the internet and this site. I'm very thankfull for all these informations !

So far I had a 6502, ROM, RAM, 6522, a small 16-keys input with a 2x12 lcd display all working on a breadboard, and currently trying to solder it all on a pcb (so at this precise moment it is not working).

NOW for my VIDEO related question:
In future, I really would like to have composite signal out, just like the old style homecomputers in the beginning 80s. (I'm thinking of our good Apple ][ I still own).
And the most important thing is: I would't like to use PIC. AtMega or similar, because I don't want to get into programming of these devices.
6502 Eprom programming is already difficult enough for me - but I got to manage it.

In the 80s there were some chips around which were called VIC or similar and basically did the job. But which one should I use ? Can I still get one of these today ? Maybe a modern version which is somehow compatible ? Where do I get ?

I'm always thinking of an Apple ][. For me a single chip-solution with a 40x23 fixed character set, optionally a lo-res graphic output, own video-RAM would be wonderful to use.

Can you please please help me ?

Greetings from Germany,
vespacla

[GARTHWILSON]

Welcome!

Those ICs are no longer made AFAIK, and they were never made for very high clock rates either; but I know there's info out there on doing your own video. A place I would start researching it is this page of one of our own prominent members, Jeff Laughton (forum name Dr Jefyll). See also the bottom of my page on displays in the 6502 primer.

[ChuckT]

There are some solutions for video because there are prebuilt video projects from other vendors like the Gameduino, Mod-VGA, the Ascii Video project, the propeller, VGA output on an STM32 Cortex M3, FTDI's Embedded Video Engine (Eve) chip which the Gameduino II is based off of, and uVGA II. There are websites that explain video signals and if you want to make a more powerful graphics engine, you can look on Mouser for Multimedia I.C.'s.

http://geoffg.net/terminal.html
http://www.4dsystems.com.au/prod.php?id=149

There are other people working in this field like the FPGA arcade and Natami team. I'm not sure if we are going to see anything from them or not.

One of the projects I am watching is this one:

An FPGA sprite graphics accelerator with a 180MHz STM32F429 controller and 640 x 360 LCD
http://andybrown.me.uk/wk/2014/06/01/ase/

[ChuckT]

There are also some TTL video projects on Kickstarter and Hackaday which are impressive but nothing I would tinker with.

[PaulF]

The simplist chip to add to a 6502 system to generate composite video (NTSC format) is the Motorola 6847. It is no longer available new, but is not difficult to get on ebay. The chip can generate a 32x16 text and block-graphic mode and 8 different lo-res graphics modes (4 in 2 colour, 4 in 4 colour.)

The simplist circuit for using this device requires an 8k RAM, a 74HC245, 2 74HC541 and 2 general purpose transistors (eg BC548 or 2N2222). This gives a monochrome output, which works well on a monochrome monitor but turns into a mess on a colour monitor because the pixel clock is at the same frequency as the colour subcarrier.

Once you have got it working, you can easily add colour encoding to give a colour output, however, the colour signal on a colour monitor is not as clear as the monochrome signal on a monochrome monitor.

See this thread viewtopic.php?f=4&t=1909 for a previous discussion of this device. If you want to use this device, I suggest you search for the Acorn Atom schematic. The Acorn Atom used a 6502 & 6847 and the schematic shows exactly how to connect the two together.

[ElEctric_EyE]

Great link Paul. I rechecked to see if the website I had found in that thread was still selling a 6845 and they are. This is a great IC for graphics only. If one need character generation then a suitably fast character ROM would have to be part of the design and a shift register.... I got into this stuff many years ago, it is very rewarding endeavor! I had used a 6845 and SND8002 with some discrete static RAMs.

I've seen a single chip lo-res board out there utilizing a PIC and custom board, but it outputs through a VGA connector.

[Aslak3]

I've had good results from the V9958. It can do 80 column text, which is what attracted me to it. It also has some decent graphical modes. Can be had for not much on eBay. One downside is it is a shrink DIP part, with 70mil spacing on the pins. Check out my blog for more info and a schematic. I'm using a 6809 but that's just a detail.

[cbscpe]

Except if you are really nostalgic and have a lot of real estate on a PCB I would suggest that you look into other solutions even if they involve programming a AVR or Microchip MCU. Arduino and Pinguino are good entry points for this. Building a Video Adapter with "discrete" logic using address multiplexors, character ROM, glue logic and a CRTC isn't easy either. Those AVR and PIC based VGA Terminals are really handy, small and cheap if a serial terminal is all you need. If you want memory mapped video than I suggest using a DP-RAM and a MCU. Believe me or not, programming a MCU is easier than programming a EPROM. Just make sure you start with a genuine programmer and not a cheap homebrew version. A AVR ISP MKII or a Pickit3 is only about 50 USD but they are supported by all tools and they work (and they are USB based). A ATMega for example is cheap and fast enough to output a composite signal and it has enough Flash to include the CGROM. With a little overclocking and a Parallel-to-Seriel Shifter (74HC166) you can even create a VGA signal. VGA has the advantage that you can connect LCD screens, in my case the only thing I have, I have no composite input device.

Cheers

Peter

[vespacla]

Hello friends,

thank you very much for all your precious help and advice !!

I've found a 6561. To be honest I'm not sure if I should be happy or not. I must have pulled it out from a VIC20 maybe 25 years ago but didn't remember that. I have read the datasheet - argh... Anyway it will take me a while even to test if it somehow works or not. I'll keep your ideas in mind !

[ChuckT]

I have never used the vic chip but I heard they are very sensitive to static electricity so you might want to buy two more.

[BigDumbDinosaur]

ChuckT wrote:

I have never used the vic chip but I heard they are very sensitive to static electricity so you might want to buy two more.

That, and the 6561 only generates 22 characters per line in text mode.

[lordbubsy]

Quote:

In future, I really would like to have composite signal out, just like the old style homecomputers in the beginning 80s. (I'm thinking of our good Apple ][ I still own).
And the most important thing is: I would't like to use PIC. AtMega or similar, because I don't want to get into programming of these devices.

If you look at the schematics of the VIC-20, you can see that the VIC needs a rather delicate timing. However, I'm a beginner and wouldn't want to use the VIC as a first choice. Like aslak3, I'd recommend the Yamaha V9958, used in the MSX2+. It's backward compatible to the Yamaha V9938 (MSX2) and Texas Instruments TMS9918 (MSX). It has a much simpler interface and separate video ram. I think the chance of success is much higher. It's almost as interfacing a 6522. It has RGB out, 15kHz SCART TV. With an AD724 you could convert it to s-video / composite.

http://en.wikipedia.org/wiki/Texas_Instruments_TMS9918
http://en.wikipedia.org/wiki/Yamaha_V9938
http://en.wikipedia.org/wiki/Yamaha_V9958

The Yamaha V9958 would be your best choice of those three and available on eBay:
http://www.ebay.de/sch/i.html?_odkw=VC+ ... acat=11189

[BigDumbDinosaur]

lordbubsy wrote:

If you look at the schematics of the VIC-20, you can see that the VIC needs a rather delicate timing.

You're right about that. All of the Commodore video devices were digital houses of cards and in the case of the VICs, didn't produce enough characters per line. Plus the VICs had no intelligence whatsoever, requiring that the MPU do all of the work of managing display and color RAM.

The VDC (8563 or 8568, the latter being the better of the two) could be considered, as it does have some intelligence. However, the VDC tends to be very pricey when found, and have do their own programming demons.

In my opinion, none of the Commodore video devices were very good. Better I think to look elsewhere for video.

[HansO]

lordbubsy wrote:

The Yamaha V9958 would be your best choice of those three and available on eBay:
http://www.ebay.de/sch/i.html?_odkw=VC+ ... acat=11189

I agree, the 99x8 IC's are nice video IC's, by isolating video from the cpu. All interfacing goes through a limited number of I/O ports. That makes it in theory slow because that limits the bandwidth. But as the many MSX demo's show (Z80 4 MHz) it can do nice things.

ebay.com is a better source, enough offers from China, including the reliable utsource shop.

Note that the V9958 requires a not so common 64 pin IC socket!

[BigDumbDinosaur]

HansO wrote:

All interfacing goes through a limited number of I/O ports. That makes it in theory slow because that limits the bandwidth. But as the many MSX demo's show (Z80 4 MHz) it can do nice things.

Same principle as Commodore's VDC, but better-executed in the V9958. The latter is much more efficient in rapidly moving video RAM around, which simplifies tasks such as scrolling and clearing the screen.