6502.org

Hi all!

I'm a new poster, but have been lurking the 6502.org website, and most of the links for a long time now.

I'm working on a few simple - small - projects for which I want some video output. I'd like to output to one of my spare old apple monitors, or a TV with rca video input.

I'm having a tinsy bit of a problem though - finding info/learning how to do this without blowing up my circuit, or destroying my display (ok, so a bit of an exageration, but you get the idea)

I came across the comodore chip that was listed on the datasheet page, but I'd like something that is easily obtainable - and preferrably easily integrateable in a variety of projects.

Any suggestions / ideas / etc. would be MOST appreciated.

-Tony
KG4WFX

Have you thought of using an On Screen Graphics chip? Most use a
simple 2 or 3 wire interface and need very little support circuitry to
make a complete video character/graphics system.

Lee.

Lee,

Do you know of specific manufacturers and part numbers of such video devices with 2- or 3-wire interfaces? I looked in a few of my CD ROM data books and couldn't find any such thing. I don't know what I would look for with a search engine. I can hardly imagine them making a serial CRTC because of the severe speed limitation, but it would really be nice sometimes if all you need is a big text screen or even graphics with very little motion (as opposed to streaming video). SPI would be faster than I2C though.

Garth

Garth,

Lee may be referring to the video overlay chips used by TVs and VCR's.

Here are two links to those kind of devices:

http://www.decadenet.com/bob3/bob3.html
http://www.web-ee.com/Schematics/Video% ... %20msg.htm

The IC used in the second link is a STV5730A. It provides a 28x11 character display and a 3-wire MPU interface.

Here is a link to its datasheet:
http://www.lechner-cctv.de/stv5730a.pdf

Hope this helps, and Happy Holidays!

Daryl

That's the sort of thing I meant.

I have a (small) pile of now redundant analog satellite receivers that have that type of chip in. It shouldn't be too hard to break the connection to the internal MCU and drive the chip from an external source.

Once you've proved it works you could make up a small PCB and transfer the chip and any other components needed.

Lee.

Hi,

My first system was a Microtan which has a 32x16 video output that was generated using standard TTL , a few discrete components and a UHF modulator. There is a schematic available on http://www.ifrance.com/oric/microtan.html although it's pretty difficult to read. (Look at the 'main board' schematic.)

The only problems with it are the special character generator PROM which if memory served included a shift register and that the all clocks where derived from the system clock (750kHz) which could be a problem - I'm not sure!

Simon

I've seen that chip before - I cam across it a while back, I was hoping for something with a little more definition, or at least a little more screen realestate - say 40 col, but I may end up searching for that chip for initial experimentation.

I wish I knew enough about video signals, I've read section and found some good sites on it, I'm just having trouble with it. I've heard one can use a microcontroller (xysomething, xylinx or something like that) to do it as that chip is fast enough, but it seems that this is a very "hush" area for discussion.

I think you're thinking of Scenix microcontrollers that supposedly were good for up to 100 MIPS. Unfortunately the only website I could ever find on them was not in one of the three languages I know, and now the URL is no good anymore anyway. Maybe they had too many problems with the product and folded. The microcontroller was similar to PIC microcontrollers, but the processor in it was not quite so decrepit. It had a few advantages over the PICs so there wasn't quite as much jerry-rigging necessary to effectively implement various addressing modes, tables, etc..

The Sym computer had a way to do a one-line, 32-character display on an oscilloscope that was so simple I laughed when I first saw it. I haven't seen it work and I expect the speed and the microprocessor overhead would present considerable limitations, but you could probably take the same idea and refine it a bit. The schematic, what little there is of it, is shown in figure 4-9 of the Sym-1 manual. The explanation and the driver code is in chapter 7. I couldn't find a Sym-1 manual on 6502.org. Maybe Mike Naberezny has one and could put it up. Otherwise I can make a copy to send him for it.

Garth

I'd be most interested to see that.

I'm really wondering how it was done on a apple 2. Yeah, it was pretty low end compared to todays standards, but it is right in the alley of what I need for text output.

Heck, maybe it'd be easier to find a site that describes how to build a VGA or RGB card?

I just wish I knew what made composite video so special that there isn't a lot of info out there on it with regard to utilizing as an output from some homebrew gadget.

so far the most informative link in terms of a circuit (albiet fairly complex) is here:

http://www.hanssummers.com/computers/computers.htm


And there's this:

http://www.ee.washington.edu/conselec/C ... c/95x4.htm

mostly information, graphs, formulas and a few circuits.

Here's the Xilinx thing I came across...

http://elm-chan.org/works/crtc/report.html

And I had one other document that I can't find right now, but this is most of the more solid pieces of info I've come across so far.

I remember reading about a simple composite video output obtained by using 60Hz interrupts on a 6502 system where the processor was basically used as the CRT controller. At every interrupt, the interrupt routine would simply scan through a fixed set of addresses containing "harmless" instructions like "nop". The address and possibly some data lines were then simply decoded to provide timing signals like hsync and vsync. Since the processor is effectively doing the addressing and counting, no components were required for counting or multiplexing addresses. Of course this method couldn't be used at the same time as other interrupts were required, and processing was limited to the vertical retrace period.

For simplicity I like the 6847 chip (quite outdated now). It has all the timing "built in" so it doesn't require programming to work. it has a built in character generator, and tri-state buffers on the addresses which make address multiplexing easy. With a couple of buffers (for the cpu) a static ram, and a couple of transistors it is possible to get a composite (bw) video display.

If you like to experiment with digital circuits, I'd suggest trying FPGA's. There is a bit more of a learning curve, but once you get the hang of things you can change circuits within minutes.

A lot of hobby projects use VGA for output probably because paradoxically VGA output is easier to interface, and offers a much higher quality output. I'd guess that many of us digital types don't look forward to building and debugging the analog circuitry required for composite output.

I have come across a few circuits for composite out. I may be forced into the VGA spectrum of doing things tho - you don't happen to have any references for VGA adapter hardware design, do you? I'd just need something really simple, 320x240 max res, built in character generation would be nice

-Tony
KG4WFX

I'm looking for a company that will sell 1 or 2 STV5730 (or STV5730A). I've found a couple of places using www.findchips.com but neither has responded to my RFQ or they advertise a minimum quantity that is far higher than what I need.

If you know of an outfit that sells this chip, please let me know at doug@infoequipt.com.

If you're interested in getting ahold of one of these, maybe we should take up a collection any buy a few!

I'd be interested in one or two if you were to put together an order.

Daryl

According to the folks at Future Electronics (www.future-active.com), the STV5730A's are on backorder until April. This might give us enough time to reach the minimum order of 28 chips. Price each is about $8.00.

If you would like to put your name on the list, let me know how many you want. Or in the meantime, if somebody discovers a company that will take smaller orders, let us know.

I'm currently also working on a project that needs video output. Right now I'm using serial for my output but want to design a 40 X 24 display. If anybody has done this, let me know, I could use the help. I don't have much experience in analog circuits and could use a partner.