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MiTo_1583836
Level 5
Level 5
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I spent some time reviewing SPI as well as the latest TAG board referenced as BCM920737TAG. If I look at the document called "920737TAG03-HWUM100-R", page 14. I see the GPIO Pin 15 called "P15" on the BCM20737A1 being connected to VDDIO via R31. The document specifies the R31 being a 0 ohm resistor, it has also been confirmed with a measurement tool.

At this point it is unclear why we would connect the "P15" to VDDIO directly, is it possible to clarify the intention behind this design?

Second point, and probably the most important, is that the Spiffy2 Master sample code in WICED-Smart-Hardware-Interfaces.pdf, page 9 sets P15/PORT 0 as CS. I think we will have a problem if we run this code on the tag board. I do see a short happening here as soon as CS is going low.

Last point I couldn't confirm the R31 resistor value via the BOM, I couldn't find it in the BOM document (ref: TAG3_Manufacturer_BOM.pdf).

Is it possible to comment on this,

Thanks

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ArvindS_76
Employee
Employee
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> At this point it is unclear why we would connect the "P15" to VDDIO directly, is it possible to clarify the intention behind this design?

Most sample applications use P15 for battery level measurement. So this is an input to one of the ADC channels.

> Second point, and problbly the most important, is that the Spiffy2 Master sample code in WICED-Smart-Hardware-Interfaces.pdf, page 9 sets P15/PORT 0 as CS.

Yes, this will be a problem on the tag. Having said that, the sample apps that come with the SDK don't use P15 and use P14 instead.

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MichaelF_56
Moderator
Moderator
Moderator
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Looking into this with the Apps team.  I noticed that when I look at the 20736/7S datasheet, logical pin P15 maps to physical pin 41?  Physical pin 31 as indicated on the schematic is mapped to logical pin P2 in the datasheet (this is noted as SPI_CS (slave only) for SPI_2. I'm also not sure if R31 is populated.  Will check and find out more or ask someone from the apps team to respond.

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ArvindS_76
Employee
Employee
500 likes received 250 likes received 100 likes received

> At this point it is unclear why we would connect the "P15" to VDDIO directly, is it possible to clarify the intention behind this design?

Most sample applications use P15 for battery level measurement. So this is an input to one of the ADC channels.

> Second point, and problbly the most important, is that the Spiffy2 Master sample code in WICED-Smart-Hardware-Interfaces.pdf, page 9 sets P15/PORT 0 as CS.

Yes, this will be a problem on the tag. Having said that, the sample apps that come with the SDK don't use P15 and use P14 instead.

Thanks for the answer, I think the topic is covered.

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