d205255e_Serial_Connections___VT100_net__and_Printer_Interface_Signals_Description
[Pin] 6 [Signal] Data set ready [Mnemonic] DSR [Description] 
To VT320 For the comm line: When on, tells the VT320 that the modem is in the data mode and is ready to communicate. For the printer line: Receives DTR on this line. If DSR is present at power-up, the printer controls print operations. If DSR is not present at power-up, the terminal checks for DSR before each print operation.
Digital VT320 Serial Connections – VT100.net
Description