STM32 Bootloader via SPI

[ADoro.2]

I made a firmware download project using a factory bootloader according to AN4286. Everything works fine.

I have only one ambiguity - in the description of the bootloader in AN2606 there is a picture on which the SCK signal is pulled-down to the ground and in the description it is written that there must be a 10k resistor.

 

Please explain the need to use a pull-down of the SCK to the ground.

Is it possible to do without it?

[Peter BENSCH · Accepted solution]

If you don't connect a pull-down to SCK and, for example, boot into the bootloader without a host connected, the sensitive SCK input will interpret noise as a clock and the bootloader may assume you have a host connected.

With the pull-down connected, there will be no activity without host and the bootloader can continue to scan the list of possible interfaces.

Does it answer your question?

Regards

/Peter

[TDK]

If you can ensure SCK is driven low while the target is in bootloader mode, it is not needed.