I’m having trouble to find a ic that I can use from the serial port of an intel NUC to SPI device (LTC6820)
I will be very thankful for help
Welcome to the forum.
I don’t know of a commercially available adapter but what you are asking for is a TIA-232 to SPI adapter. (from 1960 to 1986 it was called RS-232 because it was not an adopted standard yet)
TIA-232 is non return to zero asynchronous serial with +/-3V to +/-15V signal levels. SPI is zero volt based synchronous serial usually with +3V to +5V signal levels.
It requires a microprocessor in between the two serial systems to make it work. A common method is to use a small microcontroller to read/write the two data streams and convert between them.
You might have an easier time using a USB to SPI interface with the NUC, like this one.
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Thank you for your reply Paul 
We actually have tried the MIKROE-1204 but wirhout sucess, we had signals not coming throught, our setup was this: MIKROE-1204 <>ltc6820 (iSPI to soSPI).
But we could not understand why this did not work?
Is there any IC that i can use for TIA-232 <> SPI? And make my own pcb? (It does not have to be a finished adapter)
Best regards
Sebastian.
I do not know of any single IC solution to make the conversion from asynchronous to synchronous serial.
It’s relatively easy for a synchronous serial system to be translated to an asynchronous, or a different synchronous, system. This is why there are both SPI and USB to EIA-232 adaptors and USB to SPI adaptors from multiple companies.
Going the other direction is difficult. The easiest way for most people might be to use a custom programmed Arduino.
The Universal Serial Bus is always the easiest way to get asynchronous or synchronous serial into a modern PC. However the PC software drivers and/or application code can sometimes be very tricky to get working.
Added later:
Assuming this diagram shows what you were trying to do that didn’t work.
Then I’d try getting it to work without the two LTC6820’s in the way first.
Ok i see, maybe there is not any… we have tried arduini to but the memory was to low, so we only got some cell readings 
But if we think about usb to spi instead as you mentioned, are ther only 1 possible solution? (If not using microcontroller)
Thank you very much for your good explanation and suggestions, ideas 
Almost like the picture you added, we want to use it like this pc>MCP2210>LTC6820>LTC6811
It works very good with a raspberry or orange pi but we need to use an intel NUC for stability and reliabiliy
Definitely sounds like a driver or application software problem on the NUC.
I believe I wasn’t clear on the Arduino idea. I would not have the Arduino save any readings. It would simply translate between the SPI device and PC’s. So it should only need to save a few dozen bytes of data at a time because it can throw away the data once sent out the other port.
You could also do the translation with any SBC that has TIA-232 and SPI ports.
BTW my experience is that a Raspberry Pi is just as stable and reliable as any PC. I’ve replaced all the dedicated PCs in my home and work test labs with Raspberry Pi’s.