Thank you very much for your prompt and helpful responses, both of you. Sorry if my first post was a little brief, I will try do add some more information to it.
I don't really have a nice circuit diagramm, scribbled it by hand, and I don't think, that this will be very helpful. But I made a rough schematic, to explain my point, I hope it will help you. I might do some more detailed schematic, if it is needed.
Picture 1: Connection of arduino to a serial plug via MAX232N
Picture 2: Connection of Able System Ap863-F to a serial plug
So in the two pictures are the two parts of my setup, and if i plug this thing together, it should print something - which it doesn't. The oddness about it is, that when I connect the arduino-part with my computer, I can read out everything it prints (so I guess, that the MAX232 is wired correctly) and when I plug into the printer, I can print everything via a serial console. I also tried to switch Tx and Rx at one point of the circuit, like you suggested, RuggedCircuits, but it just doesn't help.
edit: I should also have explained, that the red and green wires in the second picture are indicating, where I shortcircuited the plug in reference to this tutorial.
I did some further research in the Programmer's Guide of the printer and this is, what I found:
The default serial interface format is 9,600 baud, 8 data bits, 1 or 2 stop bits, and no parity. Other
formats can be programmed into the printer at the factory or in the field, from the host. A setup
program, suitable for use with a PC, is available from Able Systems to simplify this process.
Serial data is expected on Rx in RS-232C format with -12V meaning 'mark' or logical '1', and +12V
meaning 'space' or logical '0', with reference to the common ground. The serial data output line, Tx,
transmits XON/XOFF and status information to the host at the same baud rate and format as the
serial data input. The hardware busy line, Busy, is true (nominally -12V) when busy.
Some host equipment use a constant space condition (+12V) to indicate a reset condition or wait
state. Some battery powered host equipment present the same output signal when they go to sleep.
By default the printer will interpret this condition as a repetitive receive error, and will print multiple '?'
characters to indicate the fault. If required, the printer may be set to ignore this condition.
The printer has a nominal 20k byte buffer which enables data to be received while previous lines are
being printed. The state of the data buffer is transmitted to the host as follows:
XOFF (13HEX) sent when buffer fills to 3/4 full;
XON (11HEX) sent when buffer empties to 1/4 full; and also after a controller reset.
The hardware busy line is set when 256 bytes of space remains; and incoming data are no longer
passed to the buffer (but may be processed) when 128 bytes remain. The hardware busy line goes
ready again when 384 bytes become free. Note that the buffer can become filled with non-printable
codes, in which case the controller will go busy.
The printer always transmits an XON character when it has woken up and is ready to receive data. It
always attempts to transmit an XOFF character to the host before going to sleep. It is not necessary
to select hardware or software handshaking. Both are active at all times.
I'm sending only a few bytes at one time to the printer, so I'm not in danger of overflowing the 20k-buffer. Shouldn't I then be able to just ignore the flow control? When I control the printer with my pc via HyperControl or minicom, I choose "None" as flow control, this is the only way to get it to work, anyway. Or am I taking something about flow control (or anything else) fundamentally wrong? I have put a lot of time into other parts of the project already (e.g. it makes use of an Adafruit Waveshield), so it would be a real pity if I don't get it to work. I would be very grateful for further suggestions.
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