Serial connection can receive but can not send
Issue: When connected via serial to my device and booting up, I can receive data, but I can not send anything, i.e. no keyboard input possible during boot process.
Root causes:
- Faulty serial adapter
- No physical connection between the RX serial pin/pad on the board and the CPU
- intended by the OEM (resistor or jumper not soldered)
- unintended by user (bad soldering of pins/wires, lose plug contact, pcb trace cut/delaminated, ...)
Solutions:
- Open putty and test serial adapter by connecting RX and TX
- If what you type on the keyboard is echoed back to the screen → OK
- If not → faulty serial adapter, get a new one.
- Check the serial connection visually for continuity. In case of interruptions detected
- Solder missing resistors/jumpers → see devicepage of your device (use the wiki search or the ToH to find the devicepage)
- Make sure pins/wires are soldered correctly. Re-solder if necessary.
- Repair any cut pcb traces / delaminated pads
Links:
- In case of doubts / still not working → OpenWrt forum