[sdiy] IC solutions for implementing reconfigurable look up tables?

Tom Wiltshire tom at electricdruid.net
Sun Aug 2 12:13:12 CEST 2020

Hi Spiros,

What you’re doing sounds a lot like the "Configurable Logic Cells” from some more recent PIC processors. One example is the 16F18885, but many others have this feature too.

Despite the dedicated hardware, I don’t know if propagation delays through the CLC block would be constant. Perhaps.
My experience with NCO jitter leads me to believe that a variable delay would certainly be audible, so this point is crucial in my view.


       Electric Druid
Synth & Stompbox DIY

> On 2 Aug 2020, at 10:44, Spiros Makris <spirosmakris92 at gmail.com> wrote:
> I am prototyping an application that is based around the concept of using LUTs to calculate logic functions. 
> So far I have successfully demonstrated the concept using an atmega328 and the computational delay is within "specs" (still quite vague). One of the advantages is that this delay is constant regardless of function complexity. However, introducing the user control hardware also adds a new delay which, although small, is now variable.
> While the concept will work fine for control signals with delays up to 100-200us, my goal is to extend the operation up to the audio range, hopefully ~10-15khz. In that context, I think that the valuable delay will manifest as noise in the output spectrum. Would that be noticeable? I have no clue, yet.
> So I was trying to think of ways to implement the LUT in dedicated hardware. Ideally, a combinational logic circuit that will be addressed directly by the inputs and output the saved value directly, without any other control logic or sequence required. A second MCU that only does this task and is controlled via interrupts and serial by a central MCU (which will support the screen and controls) is one solution I can think of and it is fairly cheap - however that requires programming two controllers. 
> I am not very familiar with the memory offerings in the market (never really used one). Is there anything that I could use to implement the above? I thought of using serial in - parallel out registers and a bunch of multiplexers, but that needs quite a lot of PCB space and will be fairly expensive.
> Any ideas would be greatly appreciated!
> Spiros
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