Remote Commands
R&S
®
Spectrum Rider FPH
269
User Manual 1321.1011.02 ─ 06.00
13.1.3
Protocols
VXI-11 Basics
The VXI-11 standard is based on the ONC-RPC protocol which in turn relies on TCP/IP
as the network/transport layer. The TCP/IP network protocol and the associated net-
work services are preconfigured. 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 13-1: Example for LAN remote control based on the 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 (pro-
gram, response and low-level control messages). The abort channel is used for imme-
diate abort of the core channel; the interrupt channel transmits spontaneous service
requests of the instrument. Link setup itself is very complex. For more details, refer to
the VXI-11 specification.
Interfaces and Protocols
