[LinuxBIOS] Cheap self-built BIOS saviour for 8M/16M parts?

[Carl-Daniel Hailfinger]

On 26.02.2007 04:29, Tom Sylla wrote:
> Carl-Daniel Hailfinger wrote:
>> So you'll need:
>> * 2 identical flash chips
>> * intermediate switch (can be hardware)
> 
> You need to disconnect ID0 from the board to the ROMs also, bending the
> J-Lead of that pin on the bottom part up is possible, and it won't break
> if you do it only once. (boards sometimes short ID pins to ground, with
> no pulldown to defeat)

I'm currently pondering whether putting the two chips on top of an
PLCC32 plug might make this easier. It certainly will facilitate
removing the whole thing again and be less prone to breaking anything.
While I'm at it, another question would be about how long wires may be
at maximum (should I need them). My calculations suggest that 10cm
would still be OK with the given timings and frequencies. However, I
have no idea whether interference would already be too strong for
the signals from/to the ROM.

>> * a way to drive RST# to GND without shorting the board

Do you have any pointer how long RST# is engaged in production to switch
between the chips? I'm worried about how long is too long. The data
sheets suggest ~100ns as minimum reset time, but if I do connect both
RST# lines to a push-button, the time will probably be at least a
million times longer.

>> * serious soldering skills to solder two chips to each other
> 
> It is not that difficult. Straighten out the J-Leads on the "top" PLCC.
> Stack the parts, and just keep the solder from messing up the pins on
> the bottom part, and you are fine. Thirty-two pins soldered will be
> quite strong. You'll end up with two roms stacked up, and a jumper super
> glued to the top one. If you want to make 100, you'll want to just make
> a pcb.

Good to know.

>> Sounds nice?
>> Surely there's a catch. It can't be that easy, right? Tell me!
> 
> Production lines utilize this same feature, the bed of nails controls
> the ID pins to allow automated test and programming by using 2 LPC parts
> on the same bus. It will work fine.

Great.

Regards,
Carl-Daniel
-- 
http://www.hailfinger.org/