The P1 port is a serial port (optional) on your digital electricity meter into which you can plug an RJ-11 (Registered Jack) connector (known from telephone connections) in order to read the meter and consumption. It is not possible to send data to the port!
At the bottom of this page I have added the “Dutch Smart Meter Requirements” (DSMR) data sheets.
Not standard (see DSMR v4.04, Chapter 4.6 “signals”)
This serial port is not standard, although it works on UART TTL level, the logical values are reversed: 1=0 and 0=1, this can be solved with software, but does not always give the desired result, the solution is to do this with hardware, for example with a chip in between, often a MAX232 or 7404 is used.
According to the specification the port can handle max. 15v, so a real RS232 signal (+12v) from a “real” com port should be possible.
Plug for the P1 port.
The connector that goes into the P1 port is a RJ-11 type, 4 or 6 pin (known from the telephone lines):
Schematic representation P1 port (ESMRv5.0 P1)