Apple][VGA

Use a standard VGA monitor on the Apple ][




What does this card do
Screen shots
In which Apples can in be used?
Which monitor can I use?
How can I get it?
Further information


This is my most recent Apple ][ project.
I started this because I wanted to reduce the number of monitors on my desk, and because I wanted to design a "big" digital circuit.
On my desk there was a 23'' VGA monitor, a 14'' monochrome monitor (for 80-column text) and a 14'' multisystem TV-set (for color graphics). This was taking up a lot of space and I had to use small monitors when playing around with the Apple ][. As far as I know, this is a common setup for Apple ][ users.

What does this card do?

To adapt the VGA monitor to the Apple video output, two things need to be done:
Scan rate conversion:
The VGA horizontal scan rate every monitor can handle is 32kHz, yielding 525 lines at 60Hz refresh rate.
The Apple outputs a signal with a horizontal scan rate of approximately 16kHz. yielding 262 lines at 60Hz refresh rate. This matches the signal a standard NTSC TV can sync to.
To overcome this, every line needs to be displayed twice in the same time. This is accomplished by storing each line output by the Apple and outputting it at double speed afterwards, while storing the next line.

Color conversion
The VGA monitor uses the RGB color system, which is responsible for the high picture quality, while the Apple outputs a 1-bit stream that is interpreted as color by the analog color decoding circuit of an NTSC TV.
This became the hard part, so I started a thread on comp.sys.apple2 that showed great interest in the card and led me to a solution of the color problem.

Screen shots

In which apples can it be used?

The original Apple][VGA actually a design for the ][/][+ that has been extended to work on the Apple //e as well.
After talking to Henry Courbis from ReaciveMicro.com I redesigned part of the circuitry to allow it to run from the AUX slot only (as a daughterboard for the RAMWorks III, for example). Because the softswitches have been changed, the original Apple][VGA had to be modified as well.
The same design change also allowed for full //c support. I designed a PCB for it, tests will follow in about two weeks. It will be an external box of about 30x8x4 cm size that connects to the video expansion connector.
The //gs will not be supported, because it has a completely different video system, that puts very different requirements on the card. But I've started collecting ideas for a GS2VGA now.

Which monitor can I use?

Both CRT and LCD monitors can be used.

NTSC Apple

CRT monitor
The video timing matches the VGA 640x480@60 Hz specification. So any monitor should display it. But, the Apple's 560x192 resolution is vertically enlarged to 560x384, but will not completely fill the screen. If the monitor has enough range, the size controls can be turned all the way up to fill the screen.

LCD monitor
Because the video timing matches the VGA spec, any LCD screen should at least display a picture. But the dot clock normally used in VGA is 25MHz while the Apple][VGA uses 28.6MHz (two times the 14.3 MHz oscillator of the apple).
Any LCD monitor can handle far higher dot clocks, but it needs to be adjusted to it. They usually have a control "clock" for this purpose. Sometimes the controlling software doesn't allow you to set a "wrong" dot clock, then you're in trouble. With the dot clock set wrong, you'll see aliasing artifacts, though they are not as visible as on a //gs, because you won't have large areas of fine structure very often. Henry Courbis reported very good display on an LCD monitor after trying the sample I sent him (the one that should be presented on KansasFest)
LCD monitors usually don't have size controls, so you have to live with a picture filling only part of the screen.

Video projector / "Beamer"
The same dot clock problem like above applies, but these usually allow for more adjustment. I've never seen a beamer that doesn't allow tweaking the dot clock far enough.

PAL Apple

CRT monitor
The timing of the Apple][VGA running in a PAL Apple is actually out of range, but I have not seen any VGA monitor that cannot display it. The same picture size problem applies.
LCD monitor
This is where the fun starts! In contrast to the CRT monitor, the LCD should have no problem displaying the out-of-range signal, but it has.
I've tested 4. The first (Iiyama) displayed it, but moved a distracting out-of-range-message over the screen and didn't allow access to the OSD
The second and third were both older Belineas and both failed.
The forth I tried was also a Belina(brand new) which displays it perfectly, showing "User mode" in the OSD.
Video projector / "Beamer"
Here, again, it is unlikely that you'll have problems. There will be enough range to adjust to the timing because progressive-scan PAL has the same timing, and is common around more expensive DVD-Players.

How can I get it?

Because of the great interest I made the card ready for sale. I added some comfort features, like an autodetection feature and an adapter so that there is no longer need to tap signals from the main board. I wrote a manual with a circuit description and designed a PCB.
After some talks to Henry Courbis from reactivemicro.com I'm now redoing the design. I expect to have final prototypes in two weeks.
The price will be between $150 and $200 + shipping depending on interest. I'm cooperating with ReactiveMicro.com to simplify sales for me and for you.
If you are interested, just send email to ferdimh@gmx.de.
This is what the card looks like:

Further information

The manual I have written is available for download here.
The (alpha) software is available here.
NOTE:Parts of the manual and the software are currently outdated, because the card's design has been changed. But you can get an overview of the card's features.
If you have any questions, suggestions or remarks feel free to email me. My email address is ferdimh@gmx.de




Ferdinand Meyer-Hermann, August 2008