Well, the thread has inside the ModBus protocol used by the SMG II inverter. The command that you posted matches the ones in the protocol. Have a look.
01 03 02 04 00 1f 44 7b
01 (Device Address)
03 (Register content query)
02 04 (Register Address 0x0204 - 516 decimal, but this one is not documented in the pdf... strange)
00 1f (a number of 0x1F bytes)
44 7b (CRC16)
SMG II 5KPRS232 V1.0 (4).pdf