[coreboot] Dual flash chip mod

[Peter Stuge]

Carl-Daniel Hailfinger wrote:
> this is no longer coreboot related.

I think this is highly coreboot related.


> > A few cm should be fine but keep them as short as possible.
> >
> > You need pins 2 (7 8) (9 10 11 12) 13 14 15 16 17 24 25 28 29 31 32
> >
> > Hm, that's 12 but some are the same signal. The ID pins and MODE can
> > probably be tied to either VDD or VSS but check their connections on
> > the original chip first.
> 
> If we're dealing with FWH chips on ICH, you can solder both chips
> on top of each other with all pins except ID0. ID0 needs to be
> connected to a switch so that exactly one of them is high and the
> other one is low.

Yes, good point, the CE in this case is ID0, and it should be
switched. ID pins are internally pulled-down so the switch circuit
actually becomes trivial. Disconnect original ID0 from mainboard.
Connect middle contact of switch to VDD via a 1k resistor. Connect
each side contact of switch to ID0 on the respective chips. The three
leads to the switch can be pretty long.

If they are PLCC chips it isn't very practical to solder two chips on
top of each other, because the chip leads bend in under the chip and
do not reach the top. Every lead on the upper chip would have to be
bent to continue straight down to maybe reach the leads on the lower
chip. I don't know if the leads are actually long enough to make that
work. Also needs a few mm for the chip package on top of the existing
chip of course. Often it's easier to put the second chip somewhere
else on the board, and run wires. Yes, that needs a little more work.


//Peter