[coreboot] BIOS Savior (RD1-PMC4/8X) unavailable? Build my own?
ajg4tadpole at gmail.com
Fri Nov 9 23:31:20 CET 2012
On 09/11/12 06:29, Milo Hoffmann wrote:
> The datasheet does not include the /CE pin from the quick and dirty
> explanation. I interpret it to mean the WE# (Write Enable) pin but am
> seeking confirmation from more informed folks.
> Can anyone on the list confirm I could hook up two identical
> SST49LF004B, using the WE# pin, to a three wire switch and have a
> functioning switchable BIOS?
There is no /CE pin because these devices are very different from the
29F040 that is referenced in the link you gave. Even if they behaved
similarly, and they don't, then /WE would be the wrong choice, it would
not affect read operations at all.
The SST49LF040B can operate in two modes. One is called programmer mode
and is only used by standalone flash programming units. The other mode
is FirmWare Hub mode (FWH) and this is the mode that is used when the
chip is actually fitted to a board and so is the one that you must deal
with. In order to have multiple FWH devices all connected up without
interfering with each other you give them all a different ID by
strapping the pins ID[0:3] to different values. So what you could do is
to wire a switch to change just the bottom ID line, ID0, for each of the
two devices, strapping one to a '0' and the other to '1', flip the
switch and invert both values. You can use a DPDT switch for this.
Connect all other lines 1:1.
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