This board converts the P1 port found on Dutch Smart Energy Meters to UART, opto-isolated from the Taster module. You can find more information in the P1 Companion Standard.
This board is only compatible with DSMR 5.0, since that version is using two additional pins (therefore RJ-12 instead of RJ-11) to supply the bidirectional optocoupler.
You can find the schema here.
The (interactive) BoM can be found here.