1
\$\begingroup\$

I am planning to create a broken wire detection between a UART communication. The main idea was to check the Tx and Rx lines with a retriggerable astable Multivibrator which creates a HIGH Level on positive edges. The output of the multivibrator then goes together with the line level in an OR gate. So if the line is in idle state or sending data, it is in a HIGH state.

However, I am not sure what happens when the Rx is unconnected and I check the unconnected Rx line. Does the Rx have a LOW level (GND) then? Or does it have some unpredictable voltage level?

Maybe anyone even does have suggestions for a better approach to detect a broken wire on a hardware level?

Any advice would be much appreciated.

\$\endgroup\$
8
  • \$\begingroup\$ But you haven't said where those lines are connected and how. Is it TTL logic between chips? Are there RS232 or RS485 tranceivers? \$\endgroup\$
    – Justme
    Commented Apr 21, 2020 at 11:42
  • \$\begingroup\$ I will upload a picture to make it clear. \$\endgroup\$
    – FrüchteTony
    Commented Apr 21, 2020 at 11:52
  • \$\begingroup\$ @Justme Atm I am expecting 0V and 5V levels between the transceivers. The components' logic will be CMOS. \$\endgroup\$
    – FrüchteTony
    Commented Apr 21, 2020 at 12:19
  • \$\begingroup\$ Your picture does not show tranceivers. Which tranceivers do you mean? Or are those just two devices communicating directly without tranceivers? What devices are those? \$\endgroup\$
    – Justme
    Commented Apr 21, 2020 at 12:37
  • \$\begingroup\$ I don't have a special device or transceiver in mind. I was hoping that there was a general answer and that this circuit could be used for different devices and transceivers. But from your question I assume a general answer can't be given. It might be a wrong approch at all. \$\endgroup\$
    – FrüchteTony
    Commented Apr 21, 2020 at 12:45

1 Answer 1

Reset to default
1
\$\begingroup\$

No there is no general answer. If you use a tranceiver like MAX232, it won't give you information if RX cable is connected or not. Some RS232 tranceiver models do give information whether valid RX levels are detected. If you use direct CMOS/TTL connection, simply put a pull-down resistor and if RX line is low then there is nothing connected.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.