Keithley 2750, User Manual

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Model 2750 Multimeter/Switch System User’s Manual Remote Operations 10-19
Signal handshaking (flow control)
Signal handshaking between the controller and the instrument allows the two devices to
communicate to each other regarding being ready or not ready to receive data. The Model
2750 does not support hardware handshaking (flow control).
Software flow control is in the form of X__ON and X__OFF characters and is enabled
when XonXoFF is selected from the RS232 FLOW menu. When the input queue of the
Model 2750 becomes more than
I
full, the instrument issues an X_OFF command. The
control program should respond to this and stop sending characters until the Model 2750
issues the X_ON, which it will do once its input buffer has dropped below half-full. The
Model 2750 recognizes X_ON and X_OFF sent from the controller. An X_OFF will cause
the Model 2750 to stop outputting characters until it sees an X_ON. Incoming commands
are processed after the <CR> character is received from the controller.
NOTE For RS-232 operation, *OPC or *OPC? should be used with slow responding
commands. A list of the slowest responding commands and details on *OPC and
*OPC? are provided in
Section 12 .
XonXoFF is the FACT and *RST default flow control setting.
If NONE is the selected flow control, then there will be no signal handshaking between
the controller and the Model 2750. Data will be lost if transmitted before the receiving
device is ready.
NOTE Even with XonXoFF selected, the computer may lose data from the Model 2750
if the return string is very large (approximately 30,000 or more characters), and
one of the higher baud rates is selected. With no flow control (NONE selected),
the error occurs with a much smaller return string. Your program could provide
some type of error checking for these situations.
NOTE Another solution to the problem is to use the TRACe:DATA:SELected? <start>,
<count> command to return small portions (100 points) of a very large buffer.
With this command, you specify a buffer location (<start>) and the number of
readings to return (<count>). See
Section 6 for details.
Terminator
The Model 2750 can be configured to terminate each program message that it transmits to
the controller with any of the following combinations of <CR> and <LF>.
<CR> Carriage return
<CR+LF> Carriage return and line feed
<LF> Line feed
<LF+CR> Line feed and carriage return
2750-900-01.book Page 19 Wednesday, August 3, 2011 7:56 AM