This page here says the SCL3 (16bit) is a DLC (32bit) chip except with the extra address pins disabled.

"All known instances of 486SLC3 CPUs are reportedly in the 132pin PQFP packaging with the extra address lines not connected (a 486BL3 running in 16-bit mode)"
https://alchetron.com/IBM-386SLC

Not sure where the knowledge comes from or is 100%, but it makes sense.

Pinout is the same as 386dx.
link

pshipkov wrote on 2024-03-29, 07:48:

Pinout is the same as 386dx.
link

It can't be that simple. The 386DX has no pins assigned to A20, Flush, Ken, Barb, etc... without those cache coherency and control aren't possible. So, at a minimum, some of the N/C pins are assigned to those functions. Are the differences between the 386DX pinout and the SLC3 documented anywhere? If those differences are documented somewhere, that is all that is needed to complete the understanding of the SLC3 pinout. However, to the best of my knowledge, this isn't available anywhere.

i know. it sounds improbable on first read but thats ok. couple of us walked that path already.
if you flip through the same thread you will see what i mean.
there is another thread by @Feipoa that contains very good info as well.

I didn't look into the SLC3 specifically, but rather looked into the DLC3, or BL3. It was determined that a QFP 386DX could be removed from a PGA interposer and a BL3 installed. I didn't come up with this idea, but rather first saw an eBay listing (~3 years ago) for such a conversion and decided to investigate.

My rendition of the adaption is here: Re: Creating a voltage regulated 386 BL3 module from existing parts I decided to down regulate the voltage and add filtering caps. It was a straight one-to-one pin fitment, I put no thought into cache invalidation. The adaption just works as far as I can tell. I now have a whole system setup around this adaption.

Unfortunately, these DLC3 chips are hard to come buy and expensive.