Keyestudio KS4028 Manual page 26

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During the process of copying the downloaded hex file to the Micro: bit
main board, the yellow signal light on the back side of the board flashes.
When the copy is completed, the yellow signal light will stop flashing and
remain on.
Step 4: run the program：
After the program is uploaded to the Micro: bit main board, you could still
power it via the USB cable or change to via an external power. The 5 x 5 LED
dot matrix on the board displays the heartbeat pattern.
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