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WICED Smart Bluetooth

ShawnA_01
Employee

The IIC and SPI (aka SPIFFY1) interfaces share Pin 16 (SCL/CLK) and Pin 15 (SDA/MOSI) of the 20732 device.  Page 19 of 20732-DS104-RDS.pdf (dated 9/17/2013) states pullups are required on these open drain I/O pins.

Schematics showing the EEPROM based designs consistently remind us that pullup resistors are required on these pins.

However, some schematics showing the (SPI) Serial Flash based implementation (e.g. 920732EVAL_Q32_P3-HWUM100-RDS.pdf) do not show pullup resistors.

I *assume* the IIC or GPIO interface is the default multiplexer setting for these pins after RESET, in which case there could (?) be a window of opportunity for an input to float before the software has an opportunity to re-configure the mux to use the SPIFFY1 interface instead?

Are the resistors mandatory (?), recommended (?), or truly not needed when using a serial flash?

1 Solution
MichaelF_56
Moderator
Moderator
Apparently, the I2C spec requires a pull up on SCL and SDA.

In addition, it turns out that an internal pull up is not sufficient because it will not be configured until an I2C slave is detected.

View solution in original post

4 Replies
ShawnA_01
Employee
The pullups are needed even when the IIC interface is not used.
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MichaelF_56
Moderator
Moderator
Note that this click-through licensing based support forum was developed as a tool for module based implementations of the BCM20732(S).  Chip-level implementations of the BC20732 require an NDA and engagement at a local level with your Broadcom Distribution and Manufactures Representatives.

Also note that the current version of the BCM20732 datsheet is 20732-DS105-R. I verified that it contains the same inference/recommendation to external pull-ups as what was noted in your original post.

On the BCM20732S module, these two pins map to Pin 21(SCL) and Pin 22(SDA) and the Technical Reference Manual for the module indicates the implimentation of a "weak" internal pull-up resistor for pins which are noted with PU status.

Another data point is that on the BCM920732TAG_Q32 Tag board, which uses the BCM20732 chip (Schematic is available within the SDK install in the DocSchematics directory), both pins are pulled up externally to VDDIO.

At this point, Id have to assume that the external pull-up is recommended on both pins.  I will confirm internally and let you know if my assumption is correct.
0 Likes
MichaelF_56
Moderator
Moderator
Apparently, the I2C spec requires a pull up on SCL and SDA.

In addition, it turns out that an internal pull up is not sufficient because it will not be configured until an I2C slave is detected.

View solution in original post

MichaelF_56
Moderator
Moderator

To summarize this discussion.


Related to I2C and SCL/SDA, external pull-ups are required on SOC, module has them built-in (10K)