Implementing SWD over a Type A to C USB cable

[Josh]

Hi,

I want to implement SWD (and potentially UART lines) over a type A to C USB cable to talk to the NRF52832 on our board.

Currently, we only want to sink power only with no USB data. We also don't need to pass USB spec, as we are just using the receptacle for nice ID.

Does anyone have any idea of what 5-6 lines would be safe to pass through SWD and UART lines? I was thinking to use the SBU lines plus D+/D- (maybe even the SS Tx lines on the UFP side) but I am not sure how it would work if they plug it into a computer port.

Thanks!

[MartinBL]

Are you planning to blug the A side of the cable into a computer and connect the pins on the C side directly to the nRF52 with nothing in between?

[Josh]

We will connect to a debugger for debugging purposes, but we want to be able to be plug into a computer directly and still charge for end-user.

[MartinBL]

I might still be misunderstanding your intentions, but

1. There are no UART lines in USB cables. If you want to communicate with an nRF52832 through USB you will have to use some sort of USB to UART converter.
2. There are no SWD lines in USB cables. To use SWD you will need some sort of MCU to convert USB to SWD.
3. The USB Vbus voltage is 5V. You cannot power an nRF52832 device with 5V without a voltage converter regulating the voltage down to < 3.6V.

In case you are not aware the nRF52840 has USB and can be powered from Vbus.

[Josh]

Hi Martin, Yes, I understand that there are no UART lines or SWD dedicated lines in USB cables, I was wondering if I could re-purpose the SS lines for SWD if I am not using SS data. Thanks

[MartinBL]

I think I might have misunderstood your initial post. You can use any of the lines in the plug for any purposes you wish, as long as you meet the connector electrical specification. But if anybody accidentally plugs your type A connector into a computer you might destroy the computer and/or the board - We cannot speculate about this or make any guarantees if you proceed to break the standard.