Andrew Morgan wrote:
On 06/07/11 12:23, Andreas Galauner wrote:
Also the pinout is kind of "weird":
1 #CS
2 #CS
3 SI
4 NC
5 SO
6 VCC
7 SCK
8 GND
Why is CS# connected to two pins? The resistance between those two pins
is 1 Ohm, so they are connected directly. Interestingly the are
connected through a 0 Ohm resistor. Any ideas on that?
I don't know the answer, I'm just having a guess here.
It could be that one of the #CS pins is connected to the flash chip, and
the other is connected to the SPI controller (or whatever you call the
thing an SPI flash chip is connected to on a computer motherboard). If
that were the case then if the 0Ω link wasn't there you would be able to
connect an SPI chip and a switch to that port. The switch would either
short pins 1 and 2, to select the internal flash chip, or would connect
whichever #CS pin is connected to the SPI controller to the #CS pin on
the external SPI flash chip in order to select that chip instead.
Does that sound like a possibility?
Very likely. Also I would expect that #4 NC is not NC at all, it just
does not go to the SPI device. It could very well be some way to allow
safe programming of the onboard SPI device such as by putting the board
into reset.
Andrew
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