Laptop debug

Mitch Bradley wmb at laptop.org
Thu Dec 20 23:46:09 EST 2007


To add additional detail to the technique outlined below:

Here is a Digi-Key part number for an easy-to-use USB-to-serial chip: 
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=604-00043-ND

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=604-00043-ND

Here is the datasheet for the part:

http://www.ftdichip.com/Documents/DataSheets/DS_FT232R_v104.pdf

Use the schematic on page 26 of that document, except:

a) Connect VCCIO to 3V3OUT instead of to VCC (so the TXD output will be 
the right voltage for the XO serial interface)
b) Leave RTS#, CTS#, CBUS0, and CBUS3 unconnected
c) Connect RXD and TXD to the serial connector that goes to the XO

Here is a part number for an adapter that will convert the surface mount 
chip to a DIP pinout that is easier to work with:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=A735-ND

Mitch Bradley wrote:
> As an alternative to wiring up a voltage converter chip, you can instead 
> go directly to USB with a USB-to-serial chip such as a PL2303.
>
> The "traditional" arrangement is:
>
>   USB-to-serial dongle   -> DB9 -> serial cable -> DB9 -> 
> 12V-to-3.3V-voltage-translator
>
> But inside the USB-to-serial dongle there is:
>
>   USB-to-serial-chip -> 3.3V-to-12V-voltage-translator
>
> So the chain:
>
>   3.3V-to-12V-voltage-translator  -> DB9 -> serial cable -> DB9 -> 
> 12V-to-3.3V-voltage-translator
>
> is essentially a complicated hardware "no-op".
>
> There is little difference in the complexity of wiring up the 
> USB-to-serial chip versus wiring up the voltage translator chip.
>
> John Watlington wrote:
>   
>> No.  You can use a standard USB/RS-232 serial converter, but
>> you will also need a voltage translator (such as a Maxim MAX3233 ---
>> you used to be able to get free samples from Maxim) and a male and
>> female connector to connect to the board.   I'll dig up the connector
>> spec (Digikey carries them) and pinout and post them on the Wiki
>> soon.  Remind me if you are in a rush.
>>
>> The debug adapters cost us around $100 to make, due to the small
>> quantity built.  We treasure them dearly, as we sometime need 50 or
>> more in a testbed!
>>
>> wad
>>
>> On Dec 20, 2007, at 12:16 PM, Gerard J. Cerchio wrote:
>>
>>   
>>     
>>> Hi All,
>>>
>>> Do the XO's ship with the serial/USB debug adapter?
>>>
>>> If not, how do I get one?
>>>
>>> -Gerard
>>>
>>>
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>>>     
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>
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