[LinuxBIOS] ECS top hat flash - dual-bios-circuit useable elsewhere ?

[Peter Stuge]

On Sun, Apr 29, 2007 at 05:31:53PM -0500, Bari Ari wrote:
> The #CE voltage is pulled high via a pull-up resistor to the VCC
> rail of the flash device.

Yes, but is the pullup usually internally in the flash chip?


> The driving signal from the chipset is an open drain on an output
> buffer FET.

Thanks for pointing this out. There is no risk of damage on an open
drain bus as long as all "inputs" to the bus only try to sink
current.


In order to control any signal it needs to be proxied or jammed.

The former is what we've been discussing so far and will require
cutting a track and some soldering.

The latter permits solderfree chip select override and is what many
game console modchips do but for address/data/read/write instead of
chip select.

They simply drive the signal "harder" than the chipset so that even
if the chipset is sinking current the flash chip will still see a
high input.

When wanting to change what the chipset says should be 0 into a 1
externally the chipset will see a lot of current through the output
and if there's too much the output will just break unless it is
protected against short circuits.

Maybe every single output on every chip does have clamping? Then I
don't have to worry, but I think that's too good to be true..

Is it? :)


//Peter