[Mezzanine] Sensors board Rev B - call for review (v2)

Akira Tsukamoto akira.tsukamoto at linaro.org
Wed Oct 28 12:30:17 UTC 2015


Hi Grant,

I read your comments regarding I2C to Uchida-san and the comment on the doc
https://docs.google.com/document/d/1GNoC-1C1xcejgLLvgm1JbpF7blwJigXq5XIB3FvnuIE/edit#heading=h.t94cutr0c4ae

I looked the datasheet of TXS0104 which is used for level shifting from 1.8V I2C to 5V I2C.
http://www.ti.com/product/txs0104e
The block diagram of TXS0104 shows that there are 10Kohm pull-up register inside,
which is common value for regular pull-up register when converting from
open drain TTL to data bus on CMOS IC.
Also, on the datasheet, it says 2Mbps capability for open drain bus,
so it should not cause any problem.

I remember even I used "10Kohm" pull up register when I was connecting
74LS TTL to 74HC series when I did not have 74 HCT series.

So TI's 10Kohm should not be problem according to the specification,
but when I goodled about I2C transmission problem that data not reaching
to the end of I2C bus, many people have been tweaking the pull-up register
to be in between 2Kohm to 5Kohm to improve the compatibility of
sending data reaching to the end of I2C bus.
http://www.picfun.com/midi2c02.html
(sorry it is in Japanese, but only the last sentence is important)

It looks like adding 3.3Kohm next to
from B1(13) to B4(10) on TXS0104 would make the pull-up value to be 2.48Kohm,
which might improve the situation.

If you have already done modification for a pre-production run next week,
please ignore all of this. :)

I also welcome any idea or comments on this.^^

Or having extra space for adding any value on the line of B1 to B4 and
able trying different value from 2.2Kowm to 4.7Kohm for the person
who has an oscilloscope before finalizing the value for the real production
might good. ^^

Akira

On 10/28/2015 03:19 PM, Grant Likely wrote:
> On Wed, Oct 28, 2015 at 11:56 AM, David Mandala
> <david.mandala at linaro.org> wrote:
>> On 10/27/15 9:26 PM, Grant Likely wrote:
>>>
>>> On Wed, Oct 28, 2015 at 6:06 AM, David Mandala <david.mandala at linaro.org>
>>> wrote:
>>>>
>>>> On 10/27/15 1:25 PM, Grant Likely wrote:
>>>>>
>>>>>
>>>>> Second posting. I've made some changes to the design. Things to note:
>>>>> - VIO is selectable between 3.3V and 5V with a slider switch
>>>>> - A through-hole stackable header is used
>>>>> - silkscreen is cleaner
>>>>>
>>>>> I think that covers all the outstanding comments. Attached are the
>>>>> schematic, design files, and a rendering.
>>>>>
>>>>> Comments welcome. I hope to send this for a pre-production run next
>>>>> week.
>>>>>
>>>>> g.
>>>>>
>>>>> Inline image 1
>>>>
>>>>
>>>> Grant,
>>>>
>>>> This looks very nice, so +1 from me.
>>>>
>>>> Do you have a mechanical layout with measurements for each connector? If
>>>> so
>>>> I can get started on the Case additions for this now.
>>>
>>>
>>> Look a the Sensors-layout.pdf file that I sent you. All of the
>>> information you need should be there.
>>>
>>> g.
>>>
>> Grant,
>>
>> Whoops I missed that.
>>
>> That is most of what I need but P2, P3, P4, P5 are missing Y coordinates,
>> 96B_SPI, P6, SW1 are missing x and y info.
>
> Try the attached file.
>
>>
>> I'm guessing that 96B_SPI GPIO2 and I2C0 are 7mm apart from the row above
>> but it's not called out.  If so that takes care of the y for them, but still
>
> Correct
>
>> need the X for 96B_SPI it's smaller then the connectors above it.
>
> Done
>
>>
>> I am assuming that:
>> A0,                             D7
>> A1,                             D6
>> A2,     A6,     I2C1 top        D5
>> AT-I2C  GPIO3   I2C1 bottom     D4
>> respectively share the same Y offsets.
>
> Yes
>
>> I am also assuming that AT-I2C, GPIO1, I2C0 and D3 y offset is 0 the front
>> edge of the board.
>
> Nominally, yes. No guarantees though.
>
> g.
>


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