Specifications

Defining Channels
PlantScape Server and Client Configuration Guide 103
Software Flow Control (XON/XOFF)
Software flow control uses special characters in the data stream to control the
transmission and reception of data. These characters are called “XON” and
“XOFF”. Because they interfere with the data flow, these characters should not
appear in the normal data transmitted in the data stream. XON/XOFF flow control
is therefore normally used only to transmit ASCII characters. Transmission of
ASCII characters ensures that the XON and XOFF characters will not appear
within the normal data stream. Software flow control is also called XON/XOFF
handshaking.
It is possible to use software flow control in addition to hardware flow control,
but this is very uncommon.
To configure your channel to use software flow control, on the Quick Builder
Port tab for serial ports, choose either Input or Output from the XON/XOFF list:
• Input uses XON/XOFF to control the flow of data on the receive line
• Output uses XON/XOFF to control the flow of data on the transmit
line
RS-232 Hardware Flow Control (RTS/CTS)
Hardware flow control uses specialized RS-232 lines of the serial cable to
determine whether the device is ready to process incoming data. These lines are
called RTS (Request to Send) and CTS (Clear to Send). This form of flow control
is often called RTS toggle/CTS handshaking.
Using this form of flow control, the server will raise the RTS line when it wants to
transmit data. The device will raise its CTS line when it is ready to receive data.
When both the RTS and CTS lines are raised, the server will transmit data. Once
the server has finished sending data, it will lower the RTS line. The device will
then lower its CTS line. The device might also lower its CTS line if its input buffer
becomes full. If this occurs the server will stop transmitting data and will wait
until the device raises its CTS line again before recommencing transmission.
Hardware flow control has special cabling requirements. Please see “Cabling for
Stallion EasyConnection” on page 104 more details.
To configure your channel to use hardware flow control, on the Quick Builder
Port tab for serial ports, ensure Enable RTS/CTS flow control is selected.
Note Because hardware flow control uses special RS-232 lines, this type
of flow control is unavailable for RS-422 and RS-485
communications.
plscpcg.book Page 103 Monday, May 28, 2001 10:11 AM