No more reply, 4 comments deep ;(

I think there was a comment from Panu in the VLSI forum about the S040 dies.

SPI works tricky, as everything else in the chip. There is a register to disable access to any of the 4 register/memory sets. So you can write all 4 or only selected ones at the same time, same as 4 identical chips connected to an external SPI bus. For read commands only one can be enabled to give a meaningful answer.

These guys really have a bag of tricks! I guess it takes a while to understand the finer details of this ingenious chip design. I'm thinking of buying some and make a breakout board.

What kind of solder paste and flux did you use?

Try contacting VLSI sales, they sent me samples of the S010 and S040.

Yes, the datasheet is a handful, but there are some very good articles in the forum, explaining stuff in detail. And sample code, which helped me a lot. When I saw the chip, I also thought about a breakout board, but never followed up on it. I even asked around about the style.

https://www.element14.com/community/polls/2907

My shield wing turned out to be OK, so I don't need a breakout any more. I am using low temperature MG Chemical M3 #4902P solder paste for my prototypes. It is lead free and has a melting point of ~140degC. For production I use Chipquik NC191SNL15 lead free paste, very easy to work with. For flux, I have Chipquik SMD 291 no clean tack, which is great gooey stuff, but ugly residue when I don't clean it!? I like clean boards.

That's a very interesting chip for retro-computing! Do you know where it's commonly used?

By the way, you mention 640x400 in the project title and 640x480 in the details. There certainly enough RAM for the once-popular 800x600 format but are there other limitations?

I briefly browsed the data sheet and noticed that there is a memory-move command - nice! This means that even text mode with scrolling should be feasible. An 8bit µC playing "character generator" will still be a bottleneck, but that's likely still OK for that 80s feeling ;-)

Edit: I had a look at VLSI - they have a maker/small company friendly store (single quantities, PayPal!), and the team looks like it consists of the kind if Finnish people I've learned to value:

What's there not to love?

Edit2: I just found your post in the VLSI forum - from browsing that I now understand that achieving 800x600 isn't possible but who cares?
http://www.vsdsp-forum.com/phpbb/viewtopic.php?f=14&t=1798&start=10

Yes, it is a family of 2 interesting chips. Thanks for pointing out the error with the resolutions. I'll fix that to ...x480 because... VGA. The RAM distribution is 1Mbit per channel as the chip is basically 4 dies of VS23S010 in one package. Higher resolutions does decrease the colour depth as well. 

My P42-Display project #NTSC/PAL Video Display Shield uses the VS23S010 chip and I have seen this one in one retro platform but have no idea about commercial applications.

My demo of the bouncing AMIGA ball uses the memory move command. The memory mapping is very unusual as the source block does not allocate a consecutive block of RAM, but has enough bits between the lines to fill up a full line! The character map could live in the free part of the video RAM as well and use the block move for fast display.

VLSI is a nice company, they shipped directly to Elecrow for a small build for me. Panu and the other guys are super helpful in the forum.

Thanks for the explanation and details! The VS23S0x0 are a bit like 80s ingenuity with today's silicon and density (it address-space / control trade-off reminds me a bit of the Apple II).

I didn't notice the 4-dies-in-a-package thing. I'll check the datasheet again to learn why SPI still works!