I'm developing for a very limited, 8 pin LPC810 microcontroller and have to connect multiple signals on a single pin. Obviously, if there's only 1 output signal on a bus, that should be OK, but what about 2 output signals? I have 3 such cases (1st signal listed is only used in programming/debug mode, while 2nd is only used during run time):
RS-232 TX output and push button - these are OK because I've read that RS-232 can be "short circuited" indefinitely by limiting the current (I measured ~30mA)
SWDIO/SWCLK (ARM serial wire debug) and GPIO output - this is my main inquiry. I know GPIO cannot be safely shorted, so for this to work, SWDIO & SWCLK must be current limited. Is that the case? I don't want to risk breaking my Segger JLink to find out.
push button (for enabling programming mode) and GPIO output - if these were to compete, the GPIO would definitely die. But I did find a way to put them on a bus without killing the GPIO: press and hold another reset button, which makes the GPIO output a GPIO input, and then press the button. This is kind of cumbersome - is there a better way?
Note: please ignore the correctness of 2 short circuited signals - I'm assuming only the cases where 1 signal dominates the other are actual use cases.
Update Here's a diagram: