IBM 4685-L0D Setup, Operation, And Service Manual page 51

Software-flow operating mode
In the software-flow operating mode, the conditions are as follows:
On receiving a DTR signal, the scanner establishes a connection with a POS
terminal, and then enters the ready state.
The scanner decodes the labels immediately after power-on.
The scanner buffers one additional label, if desired.
The scanner sends the RTS signal and then requests that the decoded data
from the label be sent to the POS terminal.
The POS terminal controls the transmission of the decoded data by means of
the software control handshaking characters, XON/XOFF.
The scanner uses the intercharacter delay specified in the configuration.
Software-flow operating mode with timing and flow control
The handshake timing and flow control used is XON/XOFF. The software-flow
operating mode operates as follows:
The scanner decodes a label. If you have chosen beep/lamp option 1, the
scanner beeps and the lamp comes on. (For a description of the beep/lamp
function, see page 4-16).
The RTS signals to the POS terminal that data is ready for transmission.
The scanner checks whether an XOFF flow control character has been
received from the POS terminal. If one has been received, the decoded data
from the label is not transmitted.
If no XOFF has been received, the scanner begins transmitting data. If the
scanner receives an XOFF character while transmitting data, the transmission
is suspended; it is resumed only after the scanner receives an XON character
from the POS terminal.
After the last character of the message is transmitted, the RTS signal is resent.
If you have chosen beep/lamp option 2, the scanner beeps and the lamp
comes on.
Another label is decoded, to begin a repetition of the code.
For details about the software-flow operating mode, see Figure 4-2.
Chapter 4. RS-232 Scanner interface specifications
4-7