Does it mean that MK20 will pull dowm the target MCU's reset pin using a GPIO? I searched a lot and found that the break signal is to issue a long period low level on the TX pin. As the interface firmware also acts as a USB-UART bridge, will the MK20 issue a long period low level on its TX pin when received a break signal from PC? If not, how can I detect the break signal receved from PC so that I can config MK20's register to issue a break signal on its TX to target MCU? I need target MCU receive the break signal across MK20 from PC .

Thanks for your help!

Best regards

Which target do you mean specifically? I assume one of the BLE boards? Yes it will pull the reset pin low when it receives a break char.

You can only change that by rewriting its firmware, which while possible, is not exactly straightforward. I don't know for the BLE targets, but possibly you can reconfigure the reset input to GPIO input, and detect a break by detecting the reset pulse. However obviously now it won't be able to be reset anymore for programming. Using Keil uVision I have been able to erase a target in this condition, but that isn't really handy if you have to do that everytime you want to reprogram, and I don't even know if it is possible with your target.

My target is a wifi implemented ARM core MCU. To update its firmware, I first make the target MCU run its UART bootloader and then I send a break signal to its UART RX to trig the firmware update,. But it seams that the MK20 eats the break signal from PC. I don't want to reset the target MCU when MK20 received a break signal but to deliver the break signal to target MCU. So I prefer to rewrite the MK20's firmware that when it detects a break signal from PC, it just issues a break signal to target MCU. And note that the UART bootloader on target MCU is a binary provided and we can't modify it. I have tried that the CH340, a USB-UART converter, and the FTDI can deliver the break signal to target MCU. So I am intrested whether the CMSIS-DAP firmware support detecting the break signal and deliver it to target MCU.

Thanks a lot!

Best regards

Well you can search the break detection in the MK20s firmware and then change it to also send a break.