VBAT pin on bluz?


I am designing a board that I would like to be able to plug both a Photon or a Bluz into. Ideally I would like to utilize the VBAT pin on the Photon board to power the RTC. However, it seems like that pin is used for programming the Bluz.

What happens if I have a coin cell battery hooked up to that VBAT pin and a Bluz is plugged in. My guess is that would be bad. Would it be best to have a jumper or DIP switch in my design to configure which type of board is plugged in? I would rather not have to do this…


Unfortunately, you would need to use some kind of a hard switch. This is from the nrf51 Reference Manual:

11.1.1 Normal mode
The DIF module will be in normal mode after power on reset. In this mode the SWDIO/nRESET pin acts as a normal active low reset pin.

To guarantee that the device remains in normal mode, the SWDCLK line must be held low, that is, ‘0’, at all times. Failing to do so may result in the DIF entering into an unknown state and may lead to undesirable behavior and power consumption.

That pin is the SWD Clock signal, or SWDCLK. We had to break out this line or we couldn’t program the boards, and there were only so many pins we could put it on and still be compatible with the Photon.



Maybe what I will do is have a toggle switch. For the Photon I will have the battery go to vbat, and for the bluz I will have the battery go to vin.