My micro-kim goes color graphics

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My micro-kim goes color graphics

Postby Pepe » Aug Thu 25, 2011 3:27 pm

I built micro-kim some years ago when he was pretty new and ever since he has been sitting on my shelf looking pretty sad, poor thing :cry: So I decided to cheer my u-kim up and get him a gift. I sat down one weekend and designed a simple color graphics card. Based on the MC6847 and a MC1372 chip it would be as simple as possible but still useful, I'd like to be able to do at least one or two nice games for it. I decided to use a 8K SRAM and to design a simple interrupt controller that allows you to enable FS and HS interrupts individually.

Here are some pictures of my system (sorry 'bout the lousy picture quality).
color1.jpg
color1.jpg (92.92 KiB) Viewed 20303 times

color2.jpg
color2.jpg (80.03 KiB) Viewed 20303 times


The SGCC (= Super Graphics Color Card) works nicely alongside with the 32K SRAM card and the "Second 6532" card (Which of course will take care of the joystick). Hmmmm, one slot left.... I'm gonna need a sound card as well =), was thinking about a FDD card to......
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Re: My micro-kim goes color graphics

Postby Pepe » Aug Sat 27, 2011 8:40 am

I have attached the schematic here as well for anyone interested, the forum did not accept pdf files for some reason so I had to make it a zip file before uploading it.

I am a bit suspicious towards the MC1372 device. It seem impossible to get a good picture on my NTSC LCD-tv. The colors bleed heavily into each other making it hard to read some characters. The color graphic modes are okay though. I have layed out my board carefully with a good ground plane under the encoder and even used a ferrite to feed the supply voltage to it.

But all of this may just be as a result of NTSC not being a very good video format. I am going to make some tests connecting an amplifier to the chroma and lumina signals and feeding them to the SVHS input of my monitor. Hopfully this will be better and i can drop the MC1372 completely.
Attachments
Schematic.zip
This is a pdf file, rename it to schematic.pdf before trying to view it.
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Re: My micro-kim goes color graphics

Postby Pepe » Aug Sun 28, 2011 3:41 am

Forget that last part, S-Video still requires a modulated chroma signal, not the pure color video signal as in component video.
I'm going to try replacing the generic BC547/BC557 that I am currently using, to the suggested 2N4401 and 2N4403 which I understand have lower capacitance and would more suited for video applications.
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Re: My micro-kim goes color graphics

Postby Pepe » Sep Wed 07, 2011 11:30 am

I finally got the time to try out the new transistors (2N4403 and 2N4401) as suggested in the Motorola Datasheet. And although the image isn't fantastic it certainly got a lot better. Now, what I really wonder is what the Motorola guys were thinking when selecting the palette :roll: The colors are really ugly and it'll be a good reach to produce any interesting games with those colors. Ujujuj.....

I also managed to get hold of an old Keytronic keyboard that I will connect to the second RIOT, Joysticks will have to go on a second game board.
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Re: My micro-kim goes color graphics

Postby vbriel » Sep Sat 10, 2011 4:55 pm

I just wanted to chime in and say this is some really good work. I played with the 6847 about 28 years ago when I was in high school. I actually designed a little 6809 board around it but never got completely finished. I agree the colors are not the best. Look at the original trs-80 coco and their colors as they used the same chip.

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Re: My micro-kim goes color graphics

Postby Pepe » Sep Sun 11, 2011 5:47 am

Thanks Vince, I have always wanted (for some obscure reason) to make a graphics board of my own with the MC6847 and MC1372. Probably because my first real computer (not counting the ZX80) was an Acorn Atom, which used the same VDU, but without the color modulator. So I had to endure bw for several years, until I got my first Atari 800.

Anyway, I received my keyboard that will be hooked to the uKim, here's a picture of it. It comes from an old Swedish computer called ABC80.
wkbrd.jpg
uKim with keyboard.
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