I have never used function code 43 or even run into it before, but Schneider's Altivar VFD line implements it for Device ID. Schneider provides an example of query and response messages on page 39 of the Altivar Serial Modbus manual at the link below. Maybe it can help you.
https://download.schneider-electric..._manual_EN_EAV64325_01.pdf&p_Doc_Ref=EAV64325
by Munir Ahmad
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