Pin 0 digital input may be high by default on V2 micro:bit

[microbit-giles]

To reproduce:

• Go to https://microbit.org/projects/make-it-code-it/pir-movement-alarm/
• Download the transmitter HEX file and flash to micro:bit V2
• Both I and a colleague observe that the diamond is shown immediately when nothing is connected to the micro:bit. We expect nothing to be shown on the display when nothing is connected to the micro:bit. This suggests pin 0 may be floating or high by default.

The HEX file seems to work as expected on a micro:bit V1 - no diamond shown by default. Diamond is shown when 3v pin connected to pin 0, and disappears when disconnected.

Are there any mitigations we can add in code, or does this need some other kind of fix?

[martinwork]

I think it must be an old hex file with a bug that has been fixed.

I see the same problem with the downloaded hex, but not with a newly built hex.

[microbit-carlos]

Based on issue #17 V2 should be configured to match V1 and set the pins default state to pull down:

• Default pull mode seems different from V1, so getDigitalValue behaves differently #17

Looking at the source code we have the default pull configured to down in the target.json files:

codal-microbit-v2/target.json

Line 26 in 3fa546f

"DEVICE_DEFAULT_PULLMODE":"PullMode::Down",

codal-microbit-v2/target-locked.json

Line 18 in 3fa546f

"DEVICE_DEFAULT_PULLMODE": "PullMode::Down",

And the default mode is applied here:

• codal-nrf52/source/NRF52Pin.cpp#L154-L156

[microbit-carlos]

I think it must be an old hex file with a bug that has been fixed.

I see the same problem with the downloaded hex, but not with a newly built hex.

Ah, thanks @martinwork!
As this hex file is hosted in the website we'll have to update it in the CMS to a newer version of MakeCode.

[microbit-carlos]

Okay, so the issue was from an old MakeCode release and has been fixed in current CODAL, so we can close this as fixed.