I'm using both I2C interfaces on my model B. To do so, I configured GPIO 28 & 29 to be in their ALT0 function. I'd really love to switch to the A+, because it's much smaller.
I already figured out that the A+ and B+ pinouts are identical.
Question is: is it save to connect an I2C device to GPIO0/1 (ID_SD and ID_SC) which does not have an EEPROM?
I'm using a buch of these: https://www.adafruit.com/products/815 with a PCA9685 chip
I already read the Add-on board design guide:
GPIO Configuration Sequencing wrote:The one exception to this rule is ID_SC and ID_SD. On a Model B+, GPIO0 (ID_SD) and GPIO1 (ID_SC) will be switched to ALT0 (I2C-0) mode and probed for an EEPROM. These pins will revert to inputs once the probe sequence has completed.
The second paragraph kind of scares me. Am I allowed to connect my extension board? After all it's a I2C chip, but it's not an EEPROM. Am I only allowed to connect after the probing completed? And what about the pull up resistors? On the model B resistors could be configured for the GPIO pins, I read that's true for the B+ too - will that work like before?ID EEPROM wrote:Within the set of pins available on the J8 GPIO header, ID_SC and ID_SD (GPIO0/SCL and GPIO1/SDA) are reserved for board detection / identification. The only allowed connections to the ID_ pins are an ID EEPROM plus 3.9K pull up resistors. Do not connect anything else to these pins!