VGA Card on Hackaday

[Elia Mady]

Hi,

Found this on Hackaday:

VGA

Is it usable with the RC2014? What would it take to make it work?

I thought I'd ask :D

Thanks everyone,

Elia

[Brian Prenovost]

Thats a pretty cool Card!  I've been looking for a Graphics solution for the RC2014, but even though you see a few people who have managed to pull it off, it doesn't seem like it's exactly ready for prime time yet.  It's a little above my pay grade as they say.

-Brian

[michael....@gmail.com]

These are specifically designed for the RC2014 :-

 https://www.tindie.com/products/maccasoft/vga-serial-terminal-kit-for-rc2014/?pt=ac_prod_search

https://www.tindie.com/products/maccasoft/graphics-video-card-kit-for-rc2014/?pt=ac_prod_search

I see they are out of stock at present though :(

/Mike

[Phillip Stevens]

You can also try this VGA / PS/2. Using standard ROMs, it emulates an ACIA Module. There’s a thread here to read for more info on the UX Module. 

https://www.tindie.com/products/feilipu/ux-module-pcb/

As postage is a PITA from Australia, order the PCB using the Gerbers in the repository. Then you can have it in any colour. 

https://github.com/feilipu/ux_module

Phillip

Michael wrote:

These are specifically designed for the RC2014 :-

 https://www.tindie.com/products/maccasoft/vga-serial-terminal-kit-for-rc2014/?pt=ac_prod_search

https://www.tindie.com/products/maccasoft/graphics-video-card-kit-for-rc2014/?pt=ac_prod_search

I see they are out of stock at present though :(

/Mike

Found this on Hackaday:

VGA

Is it usable with the RC2014? What would it take to make it work?

I thought I'd ask :D

Thanks everyone,

Elia

--

Sent from a Mobile Device. Replies may appear terse.

[Dean Netherton]

Unless you want a modern VGA/HDMI option, have you considered some of the more retro modules?

Like the TMS9918 (https://www.tindie.com/products/mfkamprath/tms9918a-video-card-kit-for-rc2014/?pt=ac_prod_search)

And there is the module I produced, the V9958 msx https://www.tindie.com/products/dinotron/v9958-msx-video-board-for-rc2014/ , I think this one is pretty cool, but I am, rather bias 😏

Dean

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[Wesley Isacks]

I concur, Dean's V9958 is rather marvelous, and (being an MSX design) it's backwards-compatible, so you can run code for the TMS9918 on it. I'm going to get the RomWBW console running on it next. Now if only I could use the RGB output (I don't do cables, and I definitely don't do mini-coax - anybody wanna make and sell some cables?)

Regarding the VGA linked on Hackaday - it's certainly interesting, but at ~25 chips it's gonna be a *large* board, even if you use SMT parts. And that's before you add the bank-switching logic it needs to play nice with the Z80 bus. Seems like a bad fit.

-Wesley

[Alan Cox]

Regarding the VGA linked on Hackaday - it's certainly interesting, but at ~25 chips it's gonna be a *large* board, even if you use SMT parts. And that's before you add the bank-switching logic it needs to play nice with the Z80 bus. Seems like a bad fit.

It also has the problem of using a lot of memory - which means it becomes very slow to scroll for example. I think that's the bigger problem in fact because you could compact the timing chains and bus enables into programmable logic to get something akin to the video chips of the period.

I do think a chunk of the logic can go away - some of the sync timing could be loaded into the 2 unused bits of the RAM in software to eliminate a pile of gates. A 6545 can also do VGA timing and memory sharing interface. It would be an option to eliminate a lot of the glue in true retro style. The 6545 however needs to see the RAM as 16bit wide to reach VGA speed so you need a bit of different glue to make the RAM seem one way or the other according to who prods it.

Another simpler board (but at composite video rate) at  http://www.waveguide.se/?article=bitmapped-video-interface, and also has a very clean solution to sharing video memory,

(The rest of the site is a good read as Daniel built his own 6303 based system, I/O devices and even an OS for it)

The 6847 was even more integrated but only offers very basic video at composite speeds and you still need a bunch of glue for the memory sharing (or a pricy dual port RAM)

There are also a bunch of period teletext decoders, some single chip, that produce RGB out at composite timings and talk i2c the other side. Finding an RGB monitor however is a bit tricky now, and the good ones like the microvitec cub are expensive because of all the BB micro collectors/retro folks.

Alan

Alan

[Bill Shen]

I'm currently working on a simple VGA interface piggyback on a 128KB RAM.  The VGA interface consists of a 4K dual port RAM, CPLD, and 25.175MHz oscillator.  It snoops a 4K block of the 128KB RAM where 1K are font lookup tables and 3K are displayed on VGA screen as 64-column and 48-row text.  The 128K RAM plugs on a Z80 SBC (ZRCC in this case) and the VGA interface is completely invisible to the Z80 SBC.  The memory works normally except the contents of a certain block (0xA000-0xAFFF in this case) are displayed on the VGA display.  0xA000-0xABFF are texts and 0xAC00-0xAFFF are fonts.  Discussion about this design can be found here:
http://forum.6502.org/viewtopic.php?f=10&t=6502&start=15
  Bill

[Alan Cox]

On Wed, 26 May 2021 at 19:58, Bill Shen <coinst...@gmail.com> wrote:

I'm currently working on a simple VGA interface piggyback on a 128KB RAM.  The VGA interface consists of a 4K dual port RAM, CPLD, and 25.175MHz oscillator.  It snoops a 4K block of the 128KB RAM where 1K are font lookup tables and 3K are displayed on VGA screen as 64-column and 48-row text.  The 128K RAM plugs on a Z80 SBC (ZRCC in this case) and the VGA interface is completely invisible to the Z80 SBC.  The memory works normally except the contents of a certain block (0xA000-0xAFFF in this case) are displayed on the VGA display.  0xA000-0xABFF are texts and 0xAC00-0xAFFF are fonts.  Discussion about this design can be found here:

I love the form factor, although I'm not sure I could wire one like that 8)

The design looks nice and for a lot of use cases on an 8bit micro having a fast updatable font set and text characters actually works far better than bitmapped for speed - even when doing graphical games. The only thing I would say is that you want a way to turn the snoop on or off so that CP/M can run nicely and flip to and from the video in the BIOS calls.

Do you plan the PS/2 to be bitbang or not ?

How pricey is the RAM is the other question I guess - new 5v dual port memory is not cheap, which is why I've not done a 6847 card that way!

[Steve Crompton]

Awesome

I like the concept Bill - pull a standard ram chip & plug in a pin compatible  VGA Module - now that is genius

Hope to see a working prototype soon

Steve

On Wed, 26 May 2021 at 19:58, Bill Shen <coinst...@gmail.com> wrote:

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[Bill Shen]

I also like the form factor that fits into existing system RAM socket, but I'm scratching my head on how to make it easier to build in such form factor.  The obvious approach is having a daughter board that plugs into existing RAM socket, but that's so unsatisfying...

Turning off the snoop is an interesting thought.  Maybe that can be achieved by writing 0xFF to top of the font memory.

No plan for PS/2, not in the RAM expansion daughterboard format because video RAM is write only, no easy way to get data back into the RAM.  This particular design is for the memory-mapped I/O of 6502; Z80 has a separate I/O space that can mapped into the 4K video RAM plus I/O port for PS2 keyboard. 

The 4K dual port RAM, IDT71342, was $2 each from UTSource, but I noticed their price has risen 50% or more across the board.

  Bill

[Bill Shen]

Current VGA conversations reminded me that I did designed a daughterboard that plugs into existing RAM socket and snoops a region of memory as video RAM and font table.   Photo is the daughterboard plugged into ZRCC.  I still like my piggybacked prototype better; I just can't come up with an equivalent PC board approach.
https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:vgaxram
  Bill