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Re: Custom interposer module for TI486SXL2-66 PGA168 to PGA132 - HELP!

I have the same question for this

But in this case it doesn’t seem that the pin exists, I was expecting flt on the soldered cpu to be ran to a gnd pin on the cpu socket, but seems not, as the flt pin seems hard wired with no resistor to vcc5

The extra pin on ODP does nothing, should not be connected internally to anything either. It's sole purpose is to prevent ODP installation into typical 486 socket (without excessive force anyway).

The other way around, that is ODPR into ODP socket, that can be done, but Intel was "clever" and didn't want people doing it (and also wanted to sell expensive ODP/487 chips) so the pinout is slightly different. ODP has the UP output on B14, which is JTAG/TMS input on typical 486 (or NC). So it won't properly drive the FLT of the installed CPU. Well, this could be fixed by soldering a piece of wire but then ODP also has FERR on a different pin, because Intel realized this wire fix was too easy to do, so now two wires are needed.

So, is is possible to put ODPR into ODP socket? Yes, I've not tested it myself but I don't see why it wouldn't work. But you will need the mods to make it work. The UP->FLT mod is mandatory, or else both CPUs will be running and fighting for the bus. FERR is optional in the sense that the system will appear to work until some pre-486 code causes FPU exception. Well behaved 486+ code should not use FERR but rather let the CPU route the exception internally but I'm not sure at which point OSes started doing that. Anything DOS is obviously going to use the old method.

EDIT: Oh, I forgot to add that some Cyrix 486 and 5x86 CPUs might be using the otherwise unused pins, but then again an ODP socket should not be wired for Cyrix, so it should be safe.

Agree Deunan ! From what I know the ODPR 168pin will direct replace a SX/DX/DX2 using same pinout in the main CPU socket. The ODP 169pin has a few changed pins and if the board allows a 169pin ODP in main CPU or Upgrade socket you must change a few jumpers from SX/DX/DX2 for it to work.....
added: and yes the key pin is only that and does not do anything (re-checked the Intel ODPR/ODP datasheet ;p)

Btw, if this is indeed a 486 setup and the socket in question is indeed for a 487

I really do believe you can probably trick it all into working though, as a 487 is actually a full blown dx cpu, and when the 487 is installed it does take over the cpu and fpu functions. The “primary cpu” actually goes dormant.

Re: Socket 1/2/3 Tweaker

487SX 169pin socket: any way to use a normal 486DX2 there?

Yeah the best pinout guide is from Intel 486_Microprocessors_and_Related_Products_Jan95 which is a 57Mb pdf....so cannot post it but here is link:
http://www.bitsavers.org/components/intel/804 … ducts_Jan95.pdf

I seem to remember watching YT video with someone modifying board to use overdrive socket with normal CPU. I think it was IBM PS/1 or ValuePoint with soldered 486SX.

doublebuffer wrote on 2023-07-15, 19:34:

Is it possible to install DX2ODPR into the co-processor slot (when the main cpu is soldered on the main board)? The true ODP chips have an extra pin that supposedly deactivates the main cpu, so I wondered maybe there's a way to mimic that. Anyone know?

At least your main CPU is soldered, so it very likely will be the 0.8µm PQFP variant. This one introduces the power down mode and does not have the huge power draw as the first ceramic 1µm 486SX' had in tristate mode. I've written something about 486 SX power draw with activated math present MP# pin B14 here Re: The 486DX-50 (not DX2) is functionally similar to other 486 right? if I set the MB to run at 33mhz can I run it fanl
As Denuan said, it is very likely that your ODPR won't work in the 487/ODP socket due to slight changes in the pinout.

There are some pins just on the 487/ODP like A13 FERR#, A15 IGNNE#, B14 MP#
At least the NMI pin is on different positions: A15 (486SX), B15 (487SX)
This list may not be complete.

487SX 169pin socket: any way to use a normal 486DX2 there?