[coreboot] LPCflasher Wiki Page
joe at settoplinux.org
Tue Nov 25 05:46:32 CET 2008
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 3.3V.
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 always
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 - 0.5V
of 3.3V :-(
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