The Scan Magic (SD/FF) in pictures

Zetr0

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Hello there my fellow AmiBayers,

Wow this is most certainly a while since I started a new thread, so I thought this information should be re-usable for fellow forum chummies

So for the non technical, what is a Scan Doubler Flicker Fixer?

Well its best to tackle both of these independently -

Scan Doubling
Simply put, this doubles the output vertical the scan rate from 15.1Khz to 31.2 KHz. It does this by copying the scan line, dublicating it and outputing it to a higher 31.2KHz refresh rate

The reason we do this is so we can display the output on devices that dont sync lower than 31.2KHz, while TV's (for the moment) will happily handle 15KHz vertical refresh signals, things like PC Monitors dont. So to use a PC VGA monitor, you need to have an output of 31KHz before the set can "pickit up"

It should be said that some PC monitors are Multi-Sync and will lock a picture at 15KHz (and lower), but it should also be noted that some (most) LCD monitors wont Sync down to less than 34KHz, as such a device like this would be incompatible.

Flicker Fixing
Have you ever wondered why some screens flicker? have you ever wondered why would the programmer want to induce violent fit inducing visuals?

Unfortunately I cannot answer the latter, but the former is quite simple...

To get more information on the screen, the computer actually uses two screens of information, and then interpolates the pictures giving more detail...

sounds a bit funky, but bare with me, lets take the Amiga Hires of 640x256 - using this interpolation technique, you can now have 640x512 pixels - so a lot more information can be presented to the user. Unfortinately this interpolated, or I should say interlaced.

imagine clasping hands together... each hand is a screens worth of pixels (640x256) and your interlocked fingers are each a scan line of information

Back in the day this was a very cheap way of adding value to a product by giving more screen modes, however to be honest, unless you ejoy fit enducing headaches, then the interlaced flickering is truly abhorrent.

So now you know what produces the flickering, how does the Flicker Fixing work?

well it requires just a little memory to hold what is called a field I would like to call it about 4 and a half scan lines ;)

So it de-interlaces these screens and re-intergrates the image as one picture of 640x512 pixels - think of it as taking a scan line from screen 1 onto output image, and then a scan line from screen 2 onto output image - this builds up a 640x512 image from two screens of 640x256.

See, it wasn't so scairy eh?
So now you know the basics, you can now see what a Scan Doubler & Flicker Fixer actually does to the output signals of your Amiga.

This thread is about the Scan Magic (aka Flicker Magic) made by DCE, so without any more delay - let me introduce the

Scan Magic: Scan Doubler Flicker Fixer


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As you can see the device is actually made up of two PCB boards, while the one on the right is what you might call the Business End, the one on the left is the Sync "pickup", thats the Vertical and Horizontal Sync collection.

This is needed to know, I suppose you could say the Shape of the image that is being generated.

Now, if you look closely to the daughter PCB on the left, in the bottom right corner of the 84way socket there is a small part filed away, this is so that it can fit flush to the motherboard, otherwise some SMD monolytic capacitors get in the way.


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In the above picture some of you may notice some familiar hardware, namely the VP101 DAC (Digital to Analog Converter) it is actually of the same family that you will find on the A1200 and A4000 motherboard, although the revision is slightly different.

The real magic of the Scan Magic is done in the MACH chip, this small CPLD performs the collecting and writing of scan lines to the memory and screen output buffer (which is very small)
Heres an overview technical drawing of the Scan Magic


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I have taken the opportunity to label holes 1 and 2 on both the daughter card and main PCB of the Scan Magic. Its a common fault for wire to snap from either end, and while wiring back up incorrectly wont damage the adapter its best to know where they go first time...
So lets look at installation -

This particular adapter is an Internal Adapter, as such it is only compatible with the A1200 and the A4000


A1200 Installation

Motherboard Orientation -
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Scan Magic Installation -
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A4000 Installation

Motherboard Orientation -
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Scan Magic Installation -
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Interestingly while this device would work on a CD32, there isn't enough physical room to actually install the device, well not without some serious hackery -

Colour Bits

I should mention (for completeness) that the Scan Magic is only an 18bit colour device - thats to say, it only has 6 bits of RED, 6 bits of Green and 6bits of Blue colour storage - where as AGA machines, like the A1200 and A4000 have infact 24 bit colour

So what does this all mean, well basically when you have a 24bit colour gradient - imagine a screen phaseing from blue to green - the picture on an 18bit output would not be as crisp, infact, you may notice some colour blocking.

However in terms of 95% of games and software, since it was written for ECS (16bit colour) you simply wont notice the difference.

So there you have it, a little story about a piece of nearly 14 year old history, thanks for reading.
 
Nice (y)

now I wonder if amigakit have any VGA connectors for the scan magic as I could do with one, after 3 attempts at making my own and failing I am reluctant to try again

oh and the joy of fields and frames, all good stuff, if u watch a film on YouTube about some Canadian tapeing the NASA video feeds and then seeing strange flashes go past the camera he has a go of explaining why they are not fake because of how video works with fields and frames indeed head sctratchin fun
 
i have a HUGE update coming for this thread.....


@Cosmic, get in touch with Hikey reg a vga cable(y)
 
a little extra info.

i had the scandoubler/ff with the external vga connector that plugs into the video out port, and in my OPO it is a terrible design!! that external board is so weak.

i have broken one one these twice:oops: just by turning the tower around or back a bit while working on the machine, the things simply snap straight down the middle!!

now thanks to Hikey (or god as he is known around here) my externals are now safe and neat internals, have a look at his work!! it's good to know these can be converted into the good versions:bowdown::bowdown:
 

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Nice :cool:

Had a word with Hikey but he is unwilling to make me up a cable so I am demoting him to demigod :p

Internal is a much better solution

I know amigakit brought out the remaining EZ stock so I am hopeing they have a cable already made up, but I must email them soon and find out, actual been meaning do this since replay in November, ho hum :whistle:
 
Awesome job there by Hikey - real pro job :bowdown::bowdown::bowdown:
 
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