Some printer don't use all pins on the RS-232connector,  so bear in mind that pins 4 & 6 need tobe looped back in order for the DP-300 to 'see' the deviceattached on the Serial Port, and list it as 'online'. For list ofall pins and functions, see list below.

9-pin    Signal   Function

1          DCD      Data Carrier Detected(DCE->DTE)

2          RXD      Received Data (DCE->DTE)

3          TXD      Transmitted Data(DTE->DCE)

4           DTR     Data Terminal Ready (DTE->DCE)

5          Gnd      Signal Ground

6           DSR     Data Set Ready (DCE->DTE)

7          RTS      Request to Send(DTE->DCE)

8          CTS      Clear to Send(DCE->DTE)

9           RI         Ring Indicator (DCE->DTE)