[beagleboard] UART0 questions?

[larbi . joubala]

hello
I am building my own am3358 based board
and i have a question on the uart0 in the schematic of the BBB
why do we need a SN74LVC2G241?
why dont connect directly to the header?
why a pull down resistor if uart0_rx and uart0_tx has already a internal 
pull up resistor?

Thanks in advance.

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[beagleboard] Vdds_ddr decoupling caps in am3358

[larbi . joubala]

I see difference between last schematic of beaglebone black and am3358 starter 
kit board concerning vdds_ddr  decoupling cap. Am3358 sk board has 21 
decoupling cap and beaglebone black uses 9 decoupling caps. The am3358 
datasheet specifies tu use min 20 decoupling caps. Why this difference?

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[beagleboard] Vdds_ddr decoupling caps am3358

[larbi . joubala]

I see difference between last schematic of beaglebone black and am3358 starter 
kit board concerning vdds_ddr  decoupling cap. Am3358 sk board has 21 
decoupling cap and beaglebone black uses 9 decoupling caps. The am3358 
datasheet specifies tu use min 20 decoupling caps. Why this difference?

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Re: [beagleboard] Vdds_ddr decoupling caps in am3358

[larbi . joubala]

ok thank you for the reply.

Le jeudi 26 mai 2016 21:08:19 UTC+2, john3909 a écrit :
>
> There are several other factors that affect decoupling:
>
> PCB Layout (smaller is better)
> Ground planes size, distance between ground planes and dielectric material 
> used
> Decoupling cap ESR
> Proximity of the decoupling caps to the power pins
> Number and size of vias connected to power pins (think of vias as a small 
> inductor)
> Copper pour profile used to connect power pins to power rail
>
> Clearly the BBB layout is optimal and that is why they managed to make the 
> board work with fewer decoupling caps.
>
> Regards,
> John
>
>
>
>
> On May 26, 2016, at 8:52 AM, Gerald Coley  > wrote:
>
> Same answer as before.
>
> BeagleBone came first. 
> Smaller board size.
> Lower cost
> And it works.
>
> Gerald
>
> On Thu, May 26, 2016 at 10:46 AM, > 
> wrote:
>
>> I see difference between last schematic of beaglebone black and am3358 
>> starter kit board concerning vdds_ddr  decoupling cap. Am3358 sk board has 
>> 21 decoupling cap and beaglebone black uses 9 decoupling caps. The am3358 
>> datasheet specifies tu use min 20 decoupling caps. Why this difference?
>>
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>
>
>
> -- 
> Gerald
>  
> ger...@beagleboard.org 
> http://beagleboard.org/
> gco...@emprodesign.com 
>
>
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[beagleboard] zero ohm resistors?

[larbi . joubala]

Hello,

I was looking at the beaglebone black schematic and I saw a lot of zero ohm 
resistors. What is the purpose of these resistors?




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[beagleboard] Max switching frequency of current on am3358

[larbi . joubala]

Hi,

  I am designing my own board based on am3358 soc. I have a question about the 
power integrity. How can i get the information of the max switching frequency 
of the current on each power pins?

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[beagleboard] Ddr3 length matching

[larbi . joubala]

Hello,

  I am designing my own board based on the am3358 and one ddr3 chip. I looked 
at the bbb project to have a example of layout and i have a question about 
length matching for the ddr3 interface. How the length matching has been done 
if different layers are used? The signal on the outer layers doesnt travel at 
the same speed as the inner layers.

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Re: [beagleboard] Ddr3 length matching

[larbi . joubala]

Ok thank you very much for the reply it is very useful.


Le jeudi 30 juin 2016 15:45:28 UTC+2, Wulf Man a écrit :
> http://referencedesigner.com/books/si/time-and-distance.php
> 
>   
> 
>   this can explain to you your issues
> 
>   
> 
>   
> 
>   
> 
>   On 6/30/2016 6:28 AM, Gerald Coley wrote:
> 
> 
> 
>   
> You use the PCB SW tools to give you the lengths of
> each trace. The distance from one layer to the next is not that
> significant and is well within the needed tolerance.
> 
> 
> 
> 
> 
> Gerald
> 
> 
> 
> 
>   
>   
> 
> 
> 
> On Sat, Jun 25, 2016 at 6:16 PM, 
>   wrote:
> 
>   Hello,
> 
> 
> 
>   I am designing my own board based on the am3358 and one
> ddr3 chip. I looked at the bbb project to have a example of
> layout and i have a question about length matching for the
> ddr3 interface. How the length matching has been done if
> different layers are used? The signal on the outer layers
> doesnt travel at the same speed as the inner layers.
> 
> 
> 
> --
> 
> For more options, visit http://beagleboard.org/discuss
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> 
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> 
>   
> 
> 
> 
> 
> 
> 
> 
> 
> 
> -- 
> 
> 
> 
>   
> 
> 
> 
>   
> 
> 
> 
>   
> 
> 
> Gerald
> 
>  
> 
> ger...@beagleboard.org
> 
> http://beagleboard.org/
> 
> gco...@emprodesign.com
> 
> 
> 
> 
>   
> 
>   
> 
>   
> 
>   
>   -- 
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