To use both SIGNAL I/O and USB control and start the test with the SIGNAL I/O connector, you need to set the trigger source to the START switch.

Follow these steps:

1. Set the trigger source to external (START switch) with the following commands:
   • TRIGger:SEQuence2:SOURce EXTernal
   • TRIGger:TEST:SOURce EXTernal
   The READY LED will temporarily turn off after sending these commands.
2. Enable the trigger function with the following commands:
   • INITiate[:IMMediate]:SEQuence2
   • INITiate[:IMMediate]:NAME TEST
   The READY LED will light up again, indicating that TOS5300 is in a “waiting for trigger” state.
3. You can now start the test with the START signal through the SIGNAL I/O connector.
4. When the test is complete, the READY LED will turn off. To prepare for the next test, send the INIT:SEQ2 command to return to the READY state.

By following these steps, you should be able to start the test through the SIGNAL I/O connector while the USB control is active.