Elecraft KXPA100 Programmers Reference - Manual (Page 22)

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^TP (Tune Poll, GET only)
GET format: ^TP;
RESPONSE format: ^TP0; (not currently tuning) or ^TP1; (tune in progress)
^TU (ATU Installed, GET only)
^TU; is used to determine if the KXAT100 Automatic Antenna Tuner option has been installed.
GET format: ^TU;
RESPONSE format: ^TU0; (ATU not detected) or ^TU1; (ATU detected).