Two different Serial Inputs

I have two different serial values coming in seperately to the RX line on the control board. Seperately they work fine but when I have both running at the same time on of the inputs gets completely ignored. Is there a way that both can work at the same time. I have both using a baud rate of 9600.

Can you tell us what the three devices are (the two TX and one RX), or at least what protocol you’re using (RS-232, TTL, other)?

So long as the transmitting devices don’t talk at the same time, you can definitely splice them together, but you’ll need to use two small diodes to keep one device from driving the RX pin while the other is trying to toggle it. Depending on your receiving device you may also need a small resistor to pull the RX pin to its idle state.

Anyway, the protocol and devices will determine the orientation of the diodes and resistor, so do let us know!



If you aren’t doing anything to synchronize your two serial sources, there’s no reason to expect your setup to work since the two sources could send data at the same time or have their bytes interleaved. Also, if you’re simply wiring two output signals together, you’re asking for destroying the transmitting devices since one device driving high and the other driving low will effectively be a short. You can do the diode thing nexisnet mentions, use a logic gate, or set up your transmitters for open-drain/open-collector operation and then wire them together.

- Jan