[coreboot] LPCflasher Wiki Page

[Joseph Smith]

On Tue, 25 Nov 2008 07:33:33 -0500, Joseph Smith <joe at settoplinux.org>
wrote:
> 
> 
> 
> On Mon, 24 Nov 2008 23:46:32 -0500, Joseph Smith <joe at settoplinux.org>
> wrote:
>>
>>
>>
>> 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 :-(
>>
> 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
> report back.
> 
BAA!!! Your right Peter.
Nope still getting high voltages from LPT signals. So here is what I am
going to do. All resisters -> gone. Schottky diodes, nope. I found that
Texas Instruments makes a 10-Bit FET bus switch with level shifting. 
http://focus.ti.com/lit/ds/symlink/sn74cbtd3861.pdf

This will work awsome, and it only costed me $0.64. The only problem is it
only comes in smaller packages and makes it hard to put on a breadboard. So
I went with the SOIC 24 package and got one of these SOIC to DIP adapters
real cheap ($1.60) on eBay. 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220296579262
This is going to work better/easier than any resistor/diode solution. I
can't wait until it gets here. Yahoo!

-- 
Thanks,
Joseph Smith
Set-Top-Linux
www.settoplinux.org