Confusion about pins 35-37 not working in Octal Flash ESP32 S3 chips

[msh911]

Hi,

ESP32 S3 datasheet specifies that pins 35-37 on octal PSRAM S3 modules are not accessible. I have confirmed that working with any octal PSRAM DevKit that I have.
However, I have designed and manufactured a PCB that has an octal PSRAM S3 module on it (ESP32-S3-WROOM-1U-N16R8) and it turns out those pins are available for any application (currently sending I2C to GPIO 36 ad 37 and it works flawlessly).

Can anyone explain why this is happening? Based on the datasheet, I should not be able to work with those pins which is true when I use the devkit, but somehow when using the module on a pcb, the pins are available.

Thanks

[ESP_Sprite]

That module doesn't have octal flash; it has octal PSRAM. If you're not using PSRAM in your program, you can use those pins as the octal PSRAM is never selected.

[msh911]

That module doesn't have octal flash; it has octal PSRAM. If you're not using PSRAM in your program, you can use those pins as the octal PSRAM is never selected.

Thanks for your response.
Sorry for the typo, I meant octal PSRAM. I corrected the post.
But I still do not understand why these pins do not work on devkit but they work on modules (based on what I have tested).

I am using the same code for both devkit and my module. I2C works on GPIO35 and 36 on my module(my pcb) but not on the devkit.

Are those pins always available on modules? they are only not accessible on devkits?


Below is from S3 data sheet:
"For modules with Octal SPI PSRAM, i.e., modules embedded with ESP32-S3R8 or ESP32-
S3R16V, pins IO35, IO36, and IO37 are connected to the Octal SPI PSRAM and are not available
for other uses."