[coreboot] [geda-user] Re: Dual SPI Flash adapter

Oliver Schinagl oliver+list at schinagl.nl
Wed Apr 18 00:26:22 CEST 2012


I've threw out half the schema and incorporated the dual FET switch. So 
far only the schema, any input appreciated! I think worked in Peter's 

I added two resistors, S1 and S2 who's purpouse is to bypass the FET 
switch if one would choose not to use one, I figured using a really 
small SMD footprint should work allright as a solder bridge?

Only downside is you'd have two 10k resistors when using a resistor 
network. When using a 100k resistor network that's less of an issue, but 
I only have some salvaged 103 ones :p One could always only solder two 
SMD resistors where the resistor network lives of course.

I'll work on the PCB the next few days, if people don't want me to throw 
everything around again :)


On 04/05/12 13:40, Oliver Schinagl wrote:
> On 04/05/12 06:16, Peter Stuge wrote:
>> Peter Stuge wrote:
>>> It's a mux on the CS/ line of two SPI flash chips.
>> Oliver, I really think you should add a real mux to the PCB, and have
>> that be "remote controlled" by the jumper or mechanical switch.
> Why is that recommended? If using a jumper cap, it shouldn't be able to
> go wrong? Chip1 active, none active, chip2 active? To which I can't
> understand why that extra component would help.
> Not that I don't believe you :p I know nothing of this stuff, but the
> goal was to make this board as simple as possible.
>> It's a small board but I think it can be done. The design I used on
> I think it would make the board a little bigger again, or actually the
> SOIC8 3306 could fit on top between the connector, so I think it may be
> possible using the same size :) Dunno if routing will be still possible :p
>> the M57SLI (see http://stuge.se/m57sli/ if curious) is shown in the
> Now the left schematic is what your motherboard does? The top right is
> what's the smallest component count and the ride side is with an easier
> switch, but higher component count?
>> attachment, but I suggest to make some improvements:
>> 1. change things around so that the switch common is GND
>> 2. look for little logic to reduce component count
>> The attachment has two suggested circuits using little logic, one
>> with only two components (3306+resistorpack) but which then requires
>> a SPDT switch, and one with three components (3306+1g14+resistorpack)
>> but which only requires shorting a jumper to ground to switch between
>> flash chips.
> Even though I am sure that the 3306 method would be better, I don't
> understand quite how and why it's needed. Also I haven't found a 3306 on
> any of my pcb's to scavenge one off :) I'd reccon the simpler design
> would allow for easier adaption?
> Finally, I notice you use 100k resistorpacks, but in a previous message
> I recall you mentioning anything between 1k and 10k should be good? (I
> happen to have a 103 resistor pack on a pcb here is my wondering :)
>> //Peter

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