1257 User Manual
EADS North America Defense
SCPI Command Basics 5-25
Test and Services, Inc.
©
2001
If the input buffer fills to capacity and RS-232 is the active
interface, several possibilities exist depending on flow control
arrangements. The 1257 instrument supports either no flow
control, software flow control (XON/XOFF), or hardware flow
control (CTS/RTS). Each scenario is described in more detail
below.
If no flow control is selected, the input buffer is full, and additional
commands are sent, the buffer will accept characters as it makes
space. It is entirely possible therefore, to have only parts of a
message queuing to the input buffer. This leaves unknown
commands on the buffer that when parsed will generate errors. For
this reason, if RS-232 communications are used without any flow
control, the user has the responsibility to insure that buffer overrun
conditions do not occur.
If software flow control is selected, and the input buffer reaches
80% capacity, the 1257 will send an XOFF character to the host.
The 80% threshold provides a reasonable safety margin to allow
for host software overhead. When the input buffer reaches the
60% capacity threshold, the 1257 will send an XON character to
the host to resume data transfer.
If hardware flow control is selected, and the input buffer is full, the
RTS signal from the 1257 will assert indicating to the remote host
than no further characters will be received. As soon as room exists
in the input buffer, the RTS signal will de-assert indicating that
room exists in the input buffer.
To make a flow control selection, select:
-----SETTINGS-----
on the top line, then select:
Type: RS-232
on the second line, and then:
Option: FlowCtrl
on the third line. Then choose the appropriate setting on the
bottom line. The default power-up state of the instrument is no flow
control. To select a different power-up state, this setting like all
other menu options can be saved to non-volatile memory. For
further details on front-panel usage refer to
Chapter 3: USING
THE FRONT PANEL CONTROLS
.
The 1257 waits for a linefeed (carriage return or carriage
return/line feed will also work in RS-232 mode if the 1257 is
configured properly) or GPIB EOI terminator before any command
is parsed. If 1024 characters are sent to the 1257 without any
Summary of Contents for 1257
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