RM5 coin acceptor help

I have a problem:
when I sent 0x00 he answers me with 0x00 and 0x1D he send me 0x00 but when I insert valide coins he gives me nothing
i connect the + 5V / gnd / rx / tx
what is there for another pin that I must use.
here is the pdf I use (manual) to better understand

thanks for all the help

Rs232english.pdf (90.5 KB)

No code, no schematic, no chance for us to help.

lg, couka

Where's your code ?

Link to product in question? (and where purchased from)

Link to datasheet?

Posted code (in code tags)?

0/3 YOU'RE OUT! :)