Functions on the printer side of serial printer cables

1. TXD (Transmit Data output pin)
   The printer sends XON/XOFF data through this pin which connects to Pin 2 on a 9-pin connector and Pin 3 on a 25-pin connector on the PC. The printer uses Pin 2. This attaches the printer's transmit pin to the PC's receive pin.

2. RXD (Receive Data input pin)
   The printer receives data (the print job) through this pin which connects to Pin 3 on a 9-pin connector and Pin 2 on a 25-pin connector on the PC. The printer uses Pin 3. This attaches the PC's transmit pin to the printer's receive pin.

3. RTS (Request To Send output pin)
   The signal level for Pin 4 is always high as long as the printer is on. This signal can be used as a source of a high signal level to enable certain functions on some printers. We recommend that you tie (solder) Pin 4 to Pins 5, 6, and 8 on the printer; however, this may not work if your printer uses these pins differently.

4. CTS, DSR, and DCD (Clear To Send, Data Set Ready, and Data Carrier Detect input pins, respectively)
   One or more of these pins may be used to enable certain functionality on the printer. We recommend that you tie (solder) these pins to Pin 4 on the printer to maintain a high signal level (see note 12).

5. DTR (Data Terminal Ready output pin)
   The printer often uses this pin for the hardware handshaking signal. If the printer supports DTR handshaking, it should use Pin 20. However, some printers use Pins 11 or 19 (or other pins besides Pin 20) to implement their handshaking.

   The handshaking pin should be connected to Pin 8 on a 9-pin connector and Pin 5 on a 25-pin connector on the PC (and also Pin 6 on either connector if you followed the recommendation in note 5).