[coreboot] LPCflasher Wiki Page
joe at settoplinux.org
Tue Nov 25 13:33:33 CET 2008
On Mon, 24 Nov 2008 23:46:32 -0500, Joseph Smith <joe at settoplinux.org>
> On Tue, 25 Nov 2008 03:36:34 +0100, Peter Stuge <peter at stuge.se> wrote:
>> Joseph Smith wrote:
>>> >> A series of 1K ohms resistors 250mW (1/4W) on data lines D0 - D6
>>> >> convert the signals from 5V to 3.3v needed by the flash chip.
>>> > This sentence and design is not so good.
>>> Ok, how about this:
>>> A series of 1K ohms resistors 250mW (1/4W) on data lines D0 ??? D6
>>> convert the signals from 5V to 3.3v needed by the flash chip.
>> This is still a bad claim. A resistor limits current and nothing
>> else. Ignoring that will harm the rest of the circuit.
>>> Any excess voltage is shunted by diodes inside the 74HC244 to its
>>> 3.3V power rail.
>> Umm, it could just break the IC. Please have a look at the data
>> sheet again to confirm my fears. Going beyond absolute maximum
>> ratings is not a good idea. Please avoid such recommendations.
> Hmm. I just hooked everything up and tested the voltages across the
> circuit. D0,D1, D2, D4, D5, and D6 are 4.13V all the way across. D3 was
> 4.37V all the way across. /Error, /SELIN, /PE, and /Ack were a solid
> The original author also put a 1k resistor across the 3.3V power rail to
> help to dissipate the current. Do you think that will help? I could
> replace the 1k resistors with schottky diodes to lower the voltage 0.6V,
> but what about the bi-directional data lines? Would I have to put 2
> schottky diodes togethor in both directions???
> Also the Voltage on the LPC and FWH chips data lines should be + or -
> of 3.3V :-(
Ahh, I think the 1k resistor across the 3.3V power rail acts as a potential
divider, I will add the 1k resistor across the 3.3V power rail, test and
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