I2c Questions

 
#11

@Jeremie,

I need your input:

Q1)
I traced the EZB pcb and it seems EZB does not have pull-ups on SDA, SCL lines, neither a resistor in series, can you confirm this ?

Regarding the Pull-Up values, several times I've used 4.7K with STM32F103, STM32F205 and other 3.3v micro-controllers.
When adding 2 devices with same values 4.7K brings down to 2.35K and still works, but if i bring down below <1.5K i had problems.

I know there are other factors:
1) cable length (let's assume we are using normal distances 30 cms)
2) I2c Bus speed

Q2) EZB I2c BUS Speed ?
*** EDIT: The default value is 100 kbit/s and can be configured in the EZ-Builder


Q3) I never heard before the recommendation for 330 to 1K, Isn't the value too low ?

Q4) Can you explain why the recommendation is different for EZB when compared to other/same 3.3 micro-controllers ?
*** EDIT 2:
STM32F205 (EZB microcontroller)
http://www.mouser.com/ds/2/389/stm32f205rb-956262.pdf
page 114
When you have long wires, the series resistors limit the slew rate, but i believe we don't need them.