Video Chips on Mouser...

[DerpymanMT]

Hi I am still selecting the chips for my Computer, and I am not sure what chip to get for the video, im putting it through a composite video signal. I cant seem to find the right chip! Is there any chips that can work with composite, and that are on mouser.com? Thank you!

[Chromatix]

Video display outputs are a big topic, and there isn't really a single chip to do it for you. I suggest starting with an LCD or e-Ink display module and working up from there. Adafruit sell a basic 16x2 character LCD kit for about $10.

[floobydust]

DerpymanMT wrote:

Hi I am still selecting the chips for my Computer, and I am not sure what chip to get for the video, im putting it through a composite video signal. I cant seem to find the right chip! Is there any chips that can work with composite, and that are on mouser.com? Thank you!

In general, you should consider the NTSC composite (RS-170) video standard as obsolete. I have several older composite monitors of course, as I'm old and have been doing the 8-bit CPU stuff for decades. However, you won't find any current video controller on Mouser that will give you a composite video signal. If you search for the CRT Controller Handbook by Gerry Kane, you'll have access to some very good information on how video is generated and the CRT controller chips of yesteryear (yesterdecade) and how they worked with older 8-bit CPUs.

In short, creating video for an older 8-bit CPU can be fairly involved. I would strongly suggest you focus on using a serial port console for your first build as you stand a high chance of success doing this, as it's really not that difficult. Once you've created an initial design and have it working with some software, you can start building some add-on hardware for other functions, native video being one of them.

In short, I'm recommending that you don't try and boil the ocean first.. start small and get some successes under your belt, then expand your project over time.

[DerpymanMT]

Oh ok, I can do that! I could use a 16x2 lcd, im mostly familiar with those! Thanks for your suggestions!

[drogon]

DerpymanMT wrote:

Oh ok, I can do that! I could use a 16x2 lcd, im mostly familiar with those! Thanks for your suggestions!

What I'd suggest is to interface a 65C22 to your system - that will give you 2 x 8-bit GPIO ports and 4 other signals to play with. It might seem like a complex chip at first, but you can run it in a very basic mode - e.g. to simply light a single LED before putting a display on - to give you lots more confidence that your system is working. It would also de-couple the timing issues with trying to connect a standard character LCD directly to the 6502 CPU bus too.

-Gordon

[DerpymanMT]

I am ordering the 65c22. I will try the single led, on each of the buses to see what would happen, I’m going to have to order more LEDs as I have ran out... But thank you again!

[drogon]

DerpymanMT wrote:

I am ordering the 65c22. I will try the single led, on each of the buses to see what would happen, I’m going to have to order more LEDs as I have ran out... But thank you again!

Never underestimate the value of a blinkenlight

On an early version of my system, I used a latch directly on the data bus - driven by the same decode signal I had planned to use for a 65C22 - while I wanted and had planned to use a 6522 in my system, I rand out of space on the stripboard version, so the latch was quick and easy.

I have also had a little board with one of those old LED bargraph devices which has been good too. See it here in this little video:

https://www.youtube.com/watch?v=0nrVC7XUgZs

Good luck with your build.

-Gordon

[Martin_H]

I agree with trying simpler output devices initially.

But after success with those, if you don't mind using modern microcontrollers there are a number of projects to add composite video using AVR's. The Propeller Chip can be used to add VGA and is also popular.

[cbmeeks]

If I could throw in my $0.02 here, I've been studying and working with displays for years. Mostly NTSC and VGA but more recently character LCD.

On my Potpourri6502 that I built last year, I left off video because I knew it would hold me back from getting my product "out the door". And I'm glad I did. My computer only had a 65C22 by default (and RAM/ROM) so it was super easy to get a "hello world" going. Once I did that, I started adding serial and character LCD.

I found the 65C22 really made interfacing to a character LCD simple. It was fun writing a display driver to handle the weird nature of how LCD's work. Mainly that they are hard-coded to 40 (or is it 80?) characters per line even if it only shows 20.

Now, you will hear lots of people say that NTSC is dead. It is. I mean, you wouldn't design a mass-produced product these days that only supported NTSC (or PAL/SECAM). But come on now. We're talking about small quantities here. I still enjoy NTSC designs and I use NTSC based computers all the time. So I say if you want to design NTSC then do it. There are lots of options and NTSC displays (while big and heavy) can still be found pretty cheap if you look. I've bought 5-6 of them from thrift stores. Usually 13" and around $5 each.

So, here is what I suggest. If you want to go NTSC only, then look into the TMS9918. It's a wonderful chip. Very well supported in the retro world and several people have designed 6502's around them. I've been keeping a collection of documentation around that chip here.

https://github.com/cbmeeks/TMS9918

The TMS9918 is pretty easy to get going and they are still easy to get from eBay for not much money. It requires complicated DRAM but there are ways around that. Look for the SRAM replacement document in my repo that shows you how to use easy, cheap SRAM with it.

Another option is to use the Parallax Propeller MCU. It's 3.3v only so you will need to deal with that. But it makes video generation almost trivial. It only requires a small EEPROM and crystal oscillator. There are tons of NTSC, PAL and VGA drivers for it. And if you run your computer around 1 MHz (recommended for beginners) then you can talk to the chip directly with little to no wait-states.

The Propeller is fast enough to drive VGA with sprites and 64 colors. Which "feels" very retro to me. 64 colors isn't a crazy amount and while VGA is slightly newer than NTSC, they are very much related and VGA monitors are dirt cheap. You can even get new monitors that still support VGA.

Keep us posted!

[8BIT]

DerpymanMT wrote:

Hi I am still selecting the chips for my Computer, and I am not sure what chip to get for the video, im putting it through a composite video signal. I cant seem to find the right chip! Is there any chips that can work with composite, and that are on mouser.com? Thank you!

I don't want to discount the rest of this discussion, but there is an ATMega88 available on Mouser for under $2 and, adding a few components and using 3 pins on the 6522 you are adding, can provide a monochrome text display via composite for under $10.

See here for details:
http://sbc.rictor.org/vid2c.html

I can program the ATmega88 for the cost of shipping.

Daryl

[BigEd]

Not 100% sure of this, but you might need to take care to use a resistor as well as an LED when driving from a chip like the 65C22.

[DerpymanMT]

I do have an arduino uno, And i did find out you can connect it to a rca cable, Maybe i could make it into a video card? Would it be possible to connect it to the VIA chip?

[Martin_H]

DerpymanMT wrote:

I do have an arduino uno, And i did find out you can connect it to a rca cable, Maybe i could make it into a video card? Would it be possible to connect it to the VIA chip?

Yes, you would use the VIA chip to bit bang SPI and send it to the Arduino. The Arduino would receive the SPI data and write it to a memory buffer. Meanwhile it would also send the pixels out to the monitor.

The video output of the Arduino is a clever hack. It uses the UART to clock out the pixels with a few resistors to establish the proper voltage levels. Here's on example:

http://www.suppertime.co.uk/blogmywiki/ ... ino-tvout/

[drogon]

DerpymanMT wrote:

I do have an arduino uno, And i did find out you can connect it to a rca cable, Maybe i could make it into a video card? Would it be possible to connect it to the VIA chip?

There are several ways to do it - one way Daryl (8bit) mentioned above. the 'generic' way is to use the Arduino TVout library.

I did a graphical version to create a 320x240 monochrome output from an ATmega1284p - it needs a bigger ATmega as that display needs 9KB of RAM. I had planned to use it with my 65C02 board but the video generation takes up about 70% of all the CPU cycles in the ATmega, so while the video was great, the communications to the 65C02 was somewhat slow.

-Gordon

[SimonJ5]

There's another example here http://geoffg.net/terminal.html that gives 80 x 24 (ish) into VGA and 44 x 15 (NTSC) or 48 x 18 (PAL) to composite. It uses a through-hole ATMEL chip - does that count?

Something that's been in the back of mind is to see if, rather than communicating via the serial is to use it as a memory mapped device - perhaps with some wait state generation from Daryl's web site.

My particular obsession is with a relatively unknown (outside of the UK) system called the Microtan 65 (from a company called Tangerine) which clocked the CPU at 750kHz and had a discrete logic video generation of 32 x 16. There was an add-on board available which used a stand-alone 6502 running at 2MHz, communicating via a couple of bytes in the memory map to give 80 x 25.

There are a couple of people who are re-casting the original designs using 'modern' replacement components only where absolutely necessary as well as providing lots of information, including circuit diagrams or both the original and new boards. They can be found at http://www.microtan.ukpc.net/. Their latest board is a 'high resolution graphics' card (as called by Tangerine back in the 80s) that gives a 256 x 256 pixel graphics board!

Simon