Keithley 708B Reference Manual page 60

Models 707B and 708B Switching Matrix Reference Manual
Dead socket connections
If a computer is connected to an instrument through TCP and the computer application is terminated
without releasing the socket, it can leave the port on the instrument "hanging". You cannot reconnect
to it without switching the power to the instrument off and then back on.
To avoid cycling power when this occurs, some instruments have a dead socket port (sometimes
known as a backdoor). The dead socket termination port is used to terminate all existing LAN
connections. This port cannot be used for command and control functions.
Use the dead socket termination port to manually disconnect a dead session on any open socket. All
existing LAN connections are terminated and closed when the connection to the dead socket
termination port is closed.
The dead socket termination port for Models 707B and 708B is 5030. Connect to this port, and then
when you disconnect, the dead port will be cleaned up (released)
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.
707B-901-01 Rev. A / August 2010
Section 2: General operation
2-41