Hello,

I'm trying to read the output of my digital energy meter with the help of a 1200 CPU in combination with the CM1241 RS232 interface.

The meter provides the different data whenever the RTS signal is high and keeps on transmitting the data as long as this is the case.

I've set the port characteristic's in the hardware and in the software.

I can run the code without any errors, but receive nothing in the buffer. When I look at the help for the RCV_PTP block there is mentioned "The sent data is only available in the receive area when the message has been acknowledged by the relevant communications partner." 

How do I get this NDR value to become high and receive data in the buffer?

Thanks in advance

I don't see this info in you post, so I'm mention this to be sure.

The output of the P1 port is a 5V TTL-signal and can not be directly connected to the CM 1241 RS232 interface.
RS232 signals are -15V / +15V and you will need to use a TTL to RS23 logic/converter to be talking to the PLC correctly. Be sure you use a proper converter. Cheap ones tend to cheat on the RS232-signal levels with the possibility that the module cant read the signals correctly. Please be aware of this.

If you aware of this, did you try to connect the P1 port directly to a computer with a open terminal to see you are receiving the telegrams from the Kwh-meter?