Troubleshooting
FT-991A CP2105 ports on macOS: why CAT doesn't answer
The port is open, but the radio stays silent. On the Mac this almost always comes down to one of the causes below. The table helps you find yours.
Symptoms and causes
| Symptom | Likely cause | Fix |
|---|---|---|
No /dev/cu.usbserial-* port at all |
Cable, USB port or missing driver | Try another cable and port. On older macOS, install the Silicon Labs VCP driver. |
| Port opens, but there is no reply at all | Standard port instead of Enhanced port | Use the other port of the pair. On our radio it was the one ending in 0. |
| Right port, still no reply | RTS is off while menu 033 CAT RTS is ENABLE | Switch RTS on in the software, or set the menu to DISABLE. |
| Garbage or nothing at all, sometimes | Baud rate differs from menu 031 CAT RATE | Set both sides to exactly the same rate. |
You only get your own command back, e.g. FA; |
Echo from the wrong device, not an answer from the radio | Check the port. A real reply carries a value, e.g. FA014074000;. |
| "Resource busy" when opening | Another program holds the port (WSJT-X, fldigi, a logger) | Only one program can open the CAT port. Close the other one, or let one program share control. |
Replies with ?;, radio reacts slowly |
Commands sent too fast (polling) | Poll less often and leave gaps between commands. |
The quick test
Send ID;. The FT-991A answers with ID0670;. If you see exactly that, port, speed and RTS are correct, and any remaining problem is in the software.
Why we wrote this
We hit every one of these problems while building MacYaesu, a native macOS app for the FT-991A. The app now recognizes the Enhanced port and offers it first. It ignores echoes and only reports "connected" after a real ID; handshake. It also writes a CAT trace with every command and reply, so you can see which of the cases above applies.
Try it with your own radio.
15-minute demo, no registration. Full version 49 CHF one-time. Requires macOS 15 or newer.
Download demo Full setup guide