Stephan Mueller wrote:
Does anybody know how, electrically, the flash is
reprogrammed? None of my books with BIOS stuff in them mention this. Is
it a MEMW or an IOW line? Either way, if you remove the BIOS and place
two of them on an appropriate ISA card with a switch on their enable
pins, it should be fine (just be careful of the switch position before
doing any flashing, of course).
Take a look at www.amd.com
They sell flash-memories (and of course, CPUs :) There you can get a
PDF-File for their Flash-chips.
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.
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.