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
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. :)