Raspberry Pi's RP2350 A4 Revision Exposes E9 Current Drain Issue
The E9 bug, an issue affecting the input mode current in the Raspberry Pi RP2350 MCU, has been addressed, providing a much-needed solution for developers working with this microcontroller. The E9 bug, officially defined as an input mode current leakage issue due to an internal pull-up that is too weak, has been causing pins to read as high even under high-impedance conditions or with weak pull-downs, necessitating smaller pull-down resistors like 8.2KΩ or less as a workaround.
The fix for this issue was announced in the July 29, 2025 Product Change Note and updated in the RP2350 A4 stepping. This hardware-level correction eliminates the improper pull-up behavior, making it possible to restore proper pull-up and pull-down functionality without the need for additional hardware.
With the introduction of the A4 stepping version of the RP2350, developers no longer need to implement external pull-down resistor modifications or worry about pins incorrectly reading high when they should not. However, it's important to note that firmware compiled with the updated pico-sdk is needed to ensure compatibility with the new stepping. Developers are advised to use pico-sdk version 2.1.0 or later for compatibility.
The A3 and new public A4 stepping versions of the RP2350 correct the erratum at the hardware level, providing drop-in compatibility with the older A2 stepping. This means that upgrading to the RP2350 A4 stepping silicon, along with updated firmware, is the official solution to erratum 9, restoring normal GPIO input behavior and eliminating the leakage issue described in the July 29 product revision note.
While the E9 saga might not be entirely over, this resolution offers a way forward for those using the RP2350 MCU. The fix addresses the root cause of the issue, ensuring that the RP2350 MCU operates as intended, making it a reliable choice for developers and hobbyists alike.
The fix for the E9 bug, a hardware-level issue in the Raspberry Pi RP2350 MCU, addresses the root cause by eliminating the improper pull-up behavior, no longer requiring developers to implement external pull-down resistor modifications. This technological advancement ensures the RP2350 MCU operates as intended, making it a reliable choice for hacking projects with a Raspberry Pi and RP2350 MCU combination.
