I'm new to the whole Linux and Raspberry world, but I have programming experience. Now I want to establish a communication between a raspberry 2, with Raspbian (Jessie) installed, and the system control of my solar installation. So the system control only puts out data (text as ASCII signs, voltage level 5V) every 60s. This data has to be collected by the raspberry and stored on an usb device.
If I test the UART communication by connecting RX and TX on the pi, everything works fine, but when I connect the system control on the raspberry (control TX to RX on pi (through voltage divider as level shifter) and GND to GND; control RX and raspberry TX are not connected -> raspberry only has to read) the raspberry counts the right amount of bytes (92 Bytes), but the data is totally wrong. For example a sent 's' is received as a 'F', a sent 'm' as a 'I' but there is no specific offset... This problems appears with my own code and with minicom.
I also tried reading this data with my notebook with an usb to rs232 converter (and this connected over a cable to UART on the system control). This works as expected using the tool "hterm" for windows 7. But when I connect this pc setup over a voltage divider to the raspberry, the same problem appears as with the system control. The baudrate is 4800 with one stop bit and ignoring the parity, so 4800 8N1. These parameters are set on all devices. The console is also disabled for the UART Port, so there is no output during boot.
I read a lot of posts in this forum containing a similar problem, but nothing seems to be solved or fits to my case. The UART settings on the raspberry should be correct, because of the flawless testing when connecting the raspberry pins RX and TX.
I would be really glad if someone could help me out.