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Dual Bios Mistake?


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#1 shepd

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Posted 15 January 2004 - 04:33 AM

I'm looking at the dual bios homebrew mod on this site here:

http://www.xbox-scen...ew-dualbios.php

And from what I can see, the switch is selecting between pin 25 (Vdd) of each chip, and also between pin 31 (LCLK)of each chip.

Is this safe? It appears to just be switching between powering alternate chips and switching between which chip receives LCLK.

Would it not work better just to switch pin 24 (INIT) between ground 3.3 V to tristate the outputs, and forget about LCLK + Vdd? It seems if you did it this way, you could set it up so you could have an unlimited number of flash chips.

Or am I confused on this? blink.gif

Thanks!

#2 [GS]EqUaTe

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Posted 15 January 2004 - 01:10 PM

You'll probably find that the chip needs to recieve those signals for one reason or another..

Although I don't know, something that you may feel is worth researching :-) (i'm too damned lazy wink.gif)

#3 shepd

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Posted 22 January 2004 - 06:49 PM

Well, I just tested it and it appears I am right.

Both chips should be connected in parallel (ie: All connections to pins from XBOX should go to pins on both chips), except for the init line.

The init line must be setup through jumpers or a switch so that one chip receives a high signal, while the other chip received a low signal. If you do this you can easily switch between two chips.

However, I haven't had any luck flashing these using the cromwell flash bios yet. My original intent was to set these up so that one chip would be write protected and loaded with cromwell, and the other not, to be loaded with Evox bios. This way if one were to put a bad flash on the evox chip, you could simply switch to the other and fix it easily.

I'll let you know if I get any further.

One other interesting item: If you want an LED for write protect, you can set it up like this if you want to keep components to a minimum:

+5 volts (not the 3.3 Volts the chip uses) ----(*RED* LED)-----(Switch)-----o-----(270 Ohm resistor)-----Ground

Connect "o" to the pins listed here:

http://www.xbox-scen...lashprotect.php

Note to the pedantic: +5 volts isn't safe for the chip. That why you have to use a Red LED. It will drop 1.8 volts. Using other LED colours may work, but some (for example, green) drop too much voltage and may not be reliable.

Next job far in the future: Figure out how to recreate #LFRAME with a PIC! biggrin.gif

#4 am3p

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Posted 22 January 2004 - 08:46 PM

I had the same idea as you, but failed sad.gif.

Pin 24 and numerous other pins are connected together to LPC pin 9 (3.3V). I'd put a SPDT in between the 2 chips but neither would work. Maybe I did it wrong :S

The modchip would work if both the 3.3V and GND Pin is disconnected.

Maybe you could spot my mistakes and point me in the right direction tongue.gif




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