80-colum expander?

orion70 · Post by **orion70** » Fri Oct 10, 2008 12:17 am

6502dude wrote:The 40/80 column display is ok and perhaps semi useful.

On downside is slows down a fair bit and it is only mono chrome display.

Text scrolling is also a bit more jerky than standard Vic-20 display.

Just out of curiosity: in 80 columns mode, characters are still clearly readable? Isn't this mode limited by the VIC's low resolution?

Mike · Post by **Mike** » Fri Oct 10, 2008 12:26 am

The VIC chip is not used for displaying the 80 character screen. Instead, another video chip resides on the cartridge, which does the display.

Michael

carlsson · Post by **carlsson** » Fri Oct 10, 2008 12:33 am

But yes, 80 column text tends to be hard to read with a composite video output, or even worse RF. It depends on the video generator, but I've tried some of my other home computers which operate in 80 columns.

ral-clan · Post by **ral-clan** » Fri Oct 10, 2008 7:29 am

A couple of us that have the Data-20 board have a dual monitor setup (dual monitors in 1982!). The regular 1702 for the VIC chip display and a high-res monochrome composite monitor for the output from the Data-20 board (an old Apple II monochrome monitor works well).

You can use both monitors simultaneously! Poke graphics to one and output text to the other, or vice versa. It's cool.

sjgray · Post by **sjgray** » Sat Oct 11, 2008 9:19 pm

About 3 years ago I built a 6545 based CRT controller (40/80 col display, ega interface, 16 foreground colours, 16 background colours, & 16k video ram).

http://sleepingelephant.com/ipw-web/bul ... c&start=15

I was thinking of connecting this to Vic-20. All I lack is spare time to pursue this as a project.

Do you still have schematics for your board? I'm curious how you did the colour capabilities. I always wondered why Commodore never made a colour PET based on the 6545... seems like only a few extra parts.

Steve

adric22 · Post by **adric22** » Sun Oct 12, 2008 8:13 am

I suppose these days a microcontroller could make an excellent 80-column display device.

ruud · Post by **ruud** » Mon Oct 13, 2008 4:28 am

[quote="sjgrayI always wondered why Commodore never made a colour PET based on the 6545... seems like only a few extra parts.[/quote]
They did, the C128. Just have a look how the registers are organized and you'll see what I meean. The problem with the 6845 is the way it addresses its memory, which makes it almost impossible to integrate it with a CPU like is done with the VIC-II video chip and the 6510 in the C64.

See next post for more.

ruud · Post by **ruud** » Mon Oct 13, 2008 4:35 am

adric22 wrote:I suppose these days a microcontroller could make an excellent 80-column display device.

I understand you want a uC to read the memory and to generate the according videosignal(s)? A good idea, but possible?

An idea that does work as it worked for me: I once made an interface that enabled me to connect 8-bit ISA cards to my C64. That enabled me to use CGA, MDA and MGA cards. Theoretically EGA and VGA cards could be used as well but they needed extra programming.
And don't forget my VIC20-PC, a VIC-20 with 65816 in a desktop case, able to use 8-bit ISA cards as well.

If one is interested I can draw a simple VIC-20 / ISA interface.

adric22 · Post by **adric22** » Mon Oct 13, 2008 9:18 am

ruud wrote: I understand you want a uC to read the memory and to generate the according videosignal(s)? A good idea, but possible?

That wasn't exactly what I had in mind. I've seen some microcontrollers used as video chips, but generally they store the screen information in their internal RAM. You would send the information to the microcontroller through a serial or parallel interface. I suppose it might be possible to set one up on the CPU BUS in a means similar to how the C128's 80-column chip is addressed.

sjgray · Post by **sjgray** » Mon Oct 13, 2008 9:46 am

ruud wrote:
sjgray wrote:I always wondered why Commodore never made a colour PET based on the 6545... seems like only a few extra parts.
They did, the C128. Just have a look how the registers are organized and you'll see what I meean. The problem with the 6845 is the way it addresses its memory, which makes it almost impossible to integrate it with a CPU like is done with the VIC-II video chip and the 6510 in the C64.

See next post for more.

Well, architecturally, the PET and the C128 are light-years apart. I'm thinking classic PET like the 4032, 8032. It should have been relatively simple to take the PET (particularly the 4032) and add a little memory for colour. You could even keep the same memory map so old software would run. Then you would have a nice backwards-compatible game machine to compete with Apple and Atari.

Though I guess when you have your own chip-making plant you want to keep making "new" chips. Sure, the C128 VDC is very 6545-like, but from what I understand it's also a flawed chip (did I hear the phone ring?

) After the VIC-II, MOS should have continued to the VIC-III for the C128 instead of waiting until the C65...

I could play "what if" forever

Steve

6502dude · Post by **6502dude** » Mon Oct 13, 2008 10:41 am

sjgray wrote:Do you still have schematics for your board? I'm curious how you did the colour capabilities. Steve

Sorry I do not have schematics. I am terrible at documenting my projects.

I used transparent memory addressing mode of 6545 CRT chip.

I use 16K for colour memory (in addition to 16K for character memory). The lower 4-bit nibble is foreground colour the upper 4 bit nibble is background colour. A 74LS257 data multiplexor is used to select between foreground and background colours. The data selection is controlled by output from 74LS165 shift register. Four bits from 74LS573 data latch allow selection of screen border colour. This is enabled on when display enable from 6545 is high. Two other bits from the 74573 latch allow selection of one of 4 different character sets stored in 27C256 EPROM. It think I have Vic-20, C64, C128, and IBM character sets currently stored.

The interface is CGA, which is TTL compatible. The four bits out from 74LS257 control red, green, blue, and intensity.

This was a fun little project along with homebrew 6502SBC project. If I ever get back to this and finish adding PS2 keyboard, plus some code to handle screen I/O & mapping, I should have a nice little stand alone 6502 with Enhanced Basic (by Lee Davison).

I think for "modern" project, it would be better to used microcontoller for Vic-20 colour video adapter. I prefer tinkering with older technology

ral-clan · Post by **ral-clan** » Mon Oct 13, 2008 1:21 pm

sjgray wrote:
About 3 years ago I built a 6545 based CRT controller (40/80 col display, ega interface, 16 foreground colours, 16 background colours, & 16k video ram).

http://sleepingelephant.com/ipw-web/bul ... c&start=15

I was thinking of connecting this to Vic-20. All I lack is spare time to pursue this as a project.
Do you still have schematics for your board? I'm curious how you did the colour capabilities. I always wondered why Commodore never made a colour PET based on the 6545... seems like only a few extra parts.

Steve

Didn't Commodore demonstrate a prototype colour version of the PET around 1980 at a trade show.? I even see to remember seeing a photograph of it....

gklinger · Post by **gklinger** » Mon Oct 13, 2008 5:43 pm

ral-clan wrote:Didn't Commodore demonstrate a prototype colour version of the PET around 1980 at a trade show.? I even see to remember seeing a photograph of it....

See here for more info.

TurtleWax · Post by **TurtleWax** » Tue Jan 27, 2009 4:08 pm

I seem to recall a program in compute gazette for the c-64 to display 80 col. Maybe you could adapt that? I am sure it would be slower than a cartridge but at least you might have better luck getting the program.
TurtleWax

carlsson · Post by **carlsson** » Wed Jan 28, 2009 2:38 am

In any case, 40 column soft generators have been around for decades (!). If I recall correctly, Sentoria posted on this site last year does up to 50 columns. That is pretty much as far you can go with the VIC chip since the pixels won't get smaller, just that you use fewer pixels per characater and widen the screen.