My questions are related to any default alternate functions that might be enabled on GPIO pins on boot and which pins are safe to use. I am specifically interested in info about the RPi Zero 2W and RPi Zero W. At this point, I don't need any alternate functions, I just need to be able to do digital reads and writes of 3.3v logic signals. I want to make sure I choose available GPIO pins that do not conflict with any alternate functions that have been enabled on the board at boot time.
Having read multiple threads on the forum and looking at the BCM2711 datasheet, I have made the following assumptions:
1. On power-up, all GPIO pins are set as inputs.
2. GPIOs 0-8 are set with active pull UP resistors.
3. GPIOs 9-27 are set with active pull DOWN resistors.
4. GPIO 2 and 3 have pull up resistors around 1.8k in order to facilitate use with I2C. All other GPIO pull up/down resisters average around 50k but can fluctuate +/- about 15k or so.
5. GPIOs 0 and 1 should not be used as they are for special functionality.
Now for my questions.....
A. Are the above assumptions correct? Is there anything to add that I haven't listed?
B. I read the following comment on a thread in this forum: "Later in the boot sequence many of them [GPIOs] are set to ALT functions, though 5 & 6 aren't in that group." Is the above statement true? If so, is there some documentation which shows which alternate functions are configured later in the boot sequence on a given GPIO pin?
C. Are there recommendations on which GPIO pins to use for basic digital input and output to reduce the risk of clobbering any default alternate functions that might be configured during OS boot or used by the Pi board itself?
Thanks!
Having read multiple threads on the forum and looking at the BCM2711 datasheet, I have made the following assumptions:
1. On power-up, all GPIO pins are set as inputs.
2. GPIOs 0-8 are set with active pull UP resistors.
3. GPIOs 9-27 are set with active pull DOWN resistors.
4. GPIO 2 and 3 have pull up resistors around 1.8k in order to facilitate use with I2C. All other GPIO pull up/down resisters average around 50k but can fluctuate +/- about 15k or so.
5. GPIOs 0 and 1 should not be used as they are for special functionality.
Now for my questions.....
A. Are the above assumptions correct? Is there anything to add that I haven't listed?
B. I read the following comment on a thread in this forum: "Later in the boot sequence many of them [GPIOs] are set to ALT functions, though 5 & 6 aren't in that group." Is the above statement true? If so, is there some documentation which shows which alternate functions are configured later in the boot sequence on a given GPIO pin?
C. Are there recommendations on which GPIO pins to use for basic digital input and output to reduce the risk of clobbering any default alternate functions that might be configured during OS boot or used by the Pi board itself?
Thanks!
Statistics: Posted by mts1969 — Tue Jan 21, 2025 6:58 pm — Replies 0 — Views 13