Serial Interface Specifications

The XON/XOFF Protocol

The RS-232 serial interface communicates using hardware and XON/XOFF flow control. Flow control helps to ensure that the computer does not send information to the printer faster than it can print.

The XON/XOFF protocol is a popular data communications protocol. When the printer’s buffer is approximately 50 percent full, it sends the ASCII code XOFF (13 Hex) to the computer to tell it to stop sending data. When there is again room (that is, space for approximately 30 percent more characters in the buffer), the printer sends the ASCII code XON (11 Hex) to the computer to tell it to resume sending data. (XON is also known as DC1; XOFF is synonymous with DC3.) If the computer does not stop sending data after it receives an XOFF, the data that overflows the buffer will be lost and the printer will halt.

The printer will send an XON code when it goes on-line to get things started. It will send an XOF code to stop the computer from sending information if the input buffer is approximately 50 percent full.

Null-Modem Cables

1 and 64
41 and 6

Where is Pin 1?

Connector: DB-9