I recently bought an Alaris Cougar motherboard to finally determine which pins on the IBM 486DLC/486BL are used for cache coherency.

The datasheet for the chipset (OPTi 82c499) is available, and using a multimeter in continuity mode I was able to determine that pin 39 is used for A20M and pin 61 is used for KEN (both are NC on the 386DX).

The 82c499 does not have a FLUSH pin (and the PGA168 socket just has a 10K pullup attached to FLUSH), but I'm fairly certain that the Blue Lightning doesn't use FLUSH because none of the remaining NC pins measured to have pullups or pulldowns attached to them.

Is it possible that the Blue Lightning only adds two pins to the base 386DX layout? Or could other pins have been repurposed/switched?

Also, if anyone has an Alaris Leopard, the same could probably be done for the 486SLC to determine which pins it uses for cache coherency. However, there's a good chance that the signals come from the PALs on the Leopard, since the OPTi 82c295 chipset used on that board doesn't have KEN or A20M pins, which could complicate things.