how can i fix error when upgrading firmware for BC660K-GL. Thanks everyone!
Immediately after you click START, do the following：
step1、Connect the BOOT pin to GND, or short circuit BOOT, and do not disconnect；
step2、Connect the RESET pin to GND, or short circuit RESET. Do not disconnect；
step3、Disconnect the RESET and GND connection；
step4、Disconnect the BOOT and GND connection；
you try again!
Can you tell me about the time to take the steps?
I do the above steps very slowly because have to connect 2 pins.
Even better if you have a link demo upgrading firmware and give for me.
Please refer to this answer
It is recommended that you weld and connect the BOOT, RESET and GND pins through wires，Follow the steps above to connect and disconnect.