Interfaces and Connectors
Operating Manual 1505.3896.12 - 14 197
9.1.3 LAN Interface
To be integrated in a LAN, the instrument is equipped with a LAN interface, consisting
of a connector, a network interface card and protocols (VXI–11). For details on the
connector and its use, refer to chapter 9.1.2.2. The network interface card supports
IEEE 802.3 for a 10 MHz Ethernet and IEEE 802.3u for a 100 MHz Ethernet.
Instrument access via VXI-11 is usually achieved from high level programming
platforms by using VISA as an intermediate abstraction layer. VISA encapsulates the
low level VXI or even GPIB function calls and thus makes the transport interface
transparent for the user. The necessary VISA library is installed when installing the
OSP Panel.
9.1.3.1 VXI-11 Protocol
The VXI–11 standard is based on the RPC protocol which in turn relies on TCP/IP as
the network/transport layer. The TCP/IP network protocol and the associated network
services are pre-configured. TCP/IP ensures connection–oriented communication,
where the order of the exchanged messages is adhered to and interrupted links are
identified. With this protocol, messages cannot be lost.
Remote control of an instrument via a network is based on standardized protocols
which follow the OSI reference model (see Fig. below).
Figure 9-2: Example for OSI Reference Model
Based on TCP/UDP, messages between the controller and the instrument are
exchanged via open network computing (ONC) – remote procedure calls (RPC). With
XDR (VXI–11), legal RPC messages are known as VXI–11 standard. Based on this
standard, messages are exchanged between the controller and the instrument. The
messages are identical with SCPI commands. They can be organized in four groups:
● Program messages (control command to the instrument)
● Response messages (values returned by the instrument)
● Service request (spontaneous queries of the instrument)
● Low–level control messages (interface messages)
A VXI–11 link between a controller and an instrument uses three channels: core, abort
and interrupt channel. Instrument control is mainly performed on the core channel
(program, response and low–level control messages). The abort channel is used for
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