Ok, I just went over a motherboard with a continuity tester. The /WE line on the flash is connected to /MEMW. The /OE line is connected to /MEMR. The flash functions as simple RAM memory. Vpp (on this motherboard, a Eurone 486 board) is connected to the middle pin of a 3-pin header. The other two pins are 5V and 12V, a jumper is installed to connect it to either voltage. The /CE line, however, is connected to the UMC UM8886 ISA bridge controller. I assume this is the case with all these chipsets. I'll check to make sure.
The CE, if i can remember, is connected to the 74 254 (an address-decoder). The 74 254 is connected to the ISA-Bus. However, perhaps the UMC has the 254 integrated. I dunno. :)
So, with any board we make, we're probably going to have to take that line from the flash socket (it's not available on the bus, obviously). No prob, just use a socket with all the appropriate pins soldered to a ribbon cable, which connects to whatever board we use, or make a board which plugs into the flash socket (bad idea, the flash is often in a rather tight place). So this is not a problem, we could switch the /CE line for selecting each chip, connect /MEMW and Vpp only to the test flash, and connect the rest of the lines (Ax, Dx, /MEMR, Vss, Vcc) to both. Told you it was easy.
I've got an experimention-Board (prototype-board) to put devices directly in a socket and build connections. I'll try to build a flash-switch myself. If i'll be successfull i'll put the wire-diagram on my page. :)
Ciao, Stephan [SpaceNet-Systems]