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Once a link has been created anything written to the device is ignored and any attempt to read
from the device returns the same identification string as the *IDN? query.
VISA Resource Name
Because of the limited support for VXI-11 (Discovery Protocol only), the instrument must be
referred to by its raw socket information when used with software packages which communicate
using a VISA resource name. For example, an instrument at IP address 192.168.0.100 would
normally have a VISA resource name of "TCPIP0::192.168.0.100::inst0::INSTR" but for this
instrument the name must be modified to read "TCPIP0::192.168.0.100::9221::SOCKET" where
9221 is the TCP port used by this instrument for control and monitoring, see below.
XML Identification Document URL
As required by the LXI standard, the instrument provides an XML identification document that
can be queried via a GET at “http://IPaddress:80/lxi/identification” that conforms to the LXI XSD
Schema (available at http://www.lxistandard.org/InstrumentIdentification/1.0 ) and the W3C
XML Schema Standards ( http://www.w3.org/XML/Schema ). This document describes the
instrument. The hostname can be used instead of the IP address if name resolution is working.
TCP Sockets
The instrument uses 1 socket on TCP port 9221 for instrument control and monitoring. Text
commands are sent to this port as defined in ‘Remote Commands’ and any replies are returned
via the same port. Any command string must contain one or more complete commands.
Multiple commands may be separated with either semicolons
“;”
or line feeds. No final
terminator is required, since the TCP frame implies a terminator, but one may be sent if desired.
11.1.6 Interface Locking
All the remote interfaces are live at all times, to remove any need to select the active interface
and to ensure that the LAN interface is always available (as demanded by the LXI standard). To
reduce the risk of the instrument being inadvertently under the control of two interfaces at once
a simple lock and release mechanism is provided in the instruction set. The lock is
automatically released where it is possible to detect disconnection, or when the Local key is
pressed. Access to the interfaces may also be restricted using the web pages.
Any interface may request to have exclusive control of the instrument by sending an “IFLOCK
1” command. The lock may only be released by sending an “IFLOCK 0” command from the
interface instance that currently has the lock, and may be queried from any interface by sending
an “IFLOCK?” command. The reply to this query will be “-1” if the lock is owned by another
interface instance, “0” if the interface is free and “1” if the lock is owned by the requesting
interface instance. Sending any command from an interface without control privileges that
attempts to change the instrument status will set bit 4 of the Standard Event Status Register
and put 200 into the Execution Error Register to indicate that there are not sufficient privileges
for the required action.
Note:
it is also possible to configure the privileges for a particular interface to either ‘read only’
or ‘no access’ from the Web page interface.
11.1.7 Status Reporting
The standard status and error reporting model described in IEEE Std. 488.2 was designed for
the GPIB interface and contains some features intended for use with the Service Request and
Parallel Poll hardware capabilities of that interface, and to accommodate its semi-duplex
operation. Although those facilities are of little use with other interfaces, this instrument makes
the full set of capabilities available to all of the interfaces. A separate set of many of the status
and error registers is maintained for each potential interface instance. The GPIB, USB and
RS232 interfaces each provide a single instance, while the LAN interface provides two: one for
the Web page and one for the TCP socket interface. Having a separate status model for each
interface instance ensures that data does not get lost, as some status query commands (e.g.
‘*ESR?’) clear the contents of a register after reading the present value.