In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 13)

2.2 Device Identification
In response to the Send Identification command, the instruments respond as follows:
1. Device address
2. SDI-12 compatibility (Version 1.3)
3. Manufacturer
4. Instrument model
5. Firmware version (100 = 1.00)
6. Serial number
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