majestyk wrote on 2022-11-30, 08:23:
Here are some pictures for one of these CPUs:
https://www.ebay.com/itm/255800842643?
Looks like R163 is missing on that one. I still can't quite make out the values of the resistors, but can almost convince myself that they're a mix of 1k and 2.2k (I think I can see 102 and 222), which would seem odd for termination as that'd make the impedance they're trying to match somewhere around 700 ohms, which sounds high. From a quick skim of the pentium pinout then it does look like those resistors are on the data bus, and probably numbered by data pin (e.g. R0 and R100 connect to D0, R23 and R123 connect to D23, etc.). Maybe they wanted the bus to be held at 3.3V ish when not being driven? No idea why though. EMC compatibility?
Also wondering about that grid of pads with no surface traces. Could be for adding capacitance to the power planes that I guess are on internal layers? I think it's all a bit odd really, curious if there are other ideas/explanations.