Section 2: General operation
Models 707B and 708B Switching Matrix Reference Manual
2-40
707B-901-01 Rev. B / January 2015
VXI-11
VXI-11 is a LAN protocol that emulates GPIB over Ethernet. It uses remote procedure calls to call
functions in the instrument for creating a link, sending data, reading data, and so on. There is also a
small header that indicates how much data is being sent. This means there is some overhead added.
Therefore VXI-11 is slower than raw socket communication. On the other hand, with VXI-11, the
programmer or driver writer does not have to confirm that the correct number of bytes have been sent
and received.
VXI-11 also supports an out-of-band channel, which allows the instrument to signal to the computer
that an event, such as a SRQ, has occurred.
VXI-11 has a limitation in that it uses broadcast packets to locate the instrument when it wants to
make a connection.
Models 707B and 708B use port 1024 for VXI-11 communication. You do not have to know this port
number to connect through VXI-11. The discovery portion of the protocol will negotiate the port
number for you. If you are trying to configure a firewall, this port number might be useful.
LAN network types
Ethernet is a type of Local Area Network (LAN) that works with a variety of transmission media. Some
of the more popular variations are 10/100BaseT, 10Base2, and 10BaseF, which use unshielded
twisted pair (UTP), coaxial cable, and optical fiber, respectively.
Most of Keithley’s instruments work with a 10/100 BaseT network and use a standard RJ-45
connector. This is an eight-wire connector, but only four wires are used: one pair to transmit and one
pair to receive data. A 10BaseT network can accommodate transmission speeds up to
10Mbits/second; 100BaseT operates at up to 100Mbits/second. Both types of networks usually
require Ethernet hubs to make connections. The exception is a one-to-one connection using a
crossover cable (see below).
The LAN connector on an instrument gives you more flexibility than GPIB and RS-232 interface
controller-subordinate configurations. Rather than connecting the instrument directly to a computer
controller in a closed loop, a LAN instrument can be connected to a TCP/IP network using its own
subnetwork, or it can be connected directly to an existing network, including a corporate intranet.
One-to-one connection
With most instruments, a one-to-one connection is done only when you are connecting a single
instrument to a single network interface card.
A one-to-one connection using a network crossover cable connection is similar to a typical RS-232
hookup using a null modem cable. The crossover cable has its receive (RX) and transmit (TX) lines
crossed to allow the receive line input to be connected to the transmit line output on the network
interfaces.
Figure 34: One-to-one connection with a crossover cable
