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RS-232 Flow Control Modes
You can select one of several flow control methods to coordinate the
transfer of data between the instrument and your computer or modem.
• None: In this mode, data is sent and received over the interface
without any flow control used. When using this method, use a slower
baud rate (< 9600 baud) and avoid sending more than 128 characters
without stopping or reading a response.
• XON/XOFF: This mode uses special characters embedded in the
data stream to control the flow. If the instrument is addressed to
send data, it continues sending data until the “
XOFF” character (13H)
is received. When the “
XON” character (11H) is received, the instrument
resumes sending data.
• DTR/DSR: In this mode, the instrument monitors the state of the
DSR (data set ready) line on the RS-232 connector. When the line
goes true, the instrument sends data over the interface. When the line
goes false, the instrument stops sending information (typically within
six characters). The instrument sets the DTR line false when the
input buffer is almost full (approximately 100 characters) and
releases the line when space is available again.
• RTS/CTS: This mode operates the same as the DTR/DSR mode but
uses the RTS (request to send) and
CTS (clear to send) lines on the
RS-232 connector instead. When the CTS line goes true, the instrument
sends data over the interface. When the line goes false, the instrument
stops sending information (typically within six characters).
The instrument sets the RTS line false when the input buffer is
almost full (approximately 100 characters) and releases the line when
space is available again.
• Modem: This mode uses the DTR/DSR and RTS/CTS lines to control
the flow of data between the instrument and a modem. When the
RS-232 interface is selected, the instrument sets the DTR line true.
The DSR line is set true when the modem is on-line. The instrument
sets the RTS line true when it is ready to receive data. The modem
sets the CTS line true when it is ready to accept data. The instrument
sets the RTS line false when the input buffer is almost full
(approximately 100 characters) and releases the line when space is
available again.
5
Chapter 5 Remote Interface Reference
RS-232 Interface Configuration
271