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6.3 Bus Remote Interface GPIB / RS-232
This section provides information on the proper use and configuration of bus remote interface.
The RS-232 remote interface is standard on 7630 but the GPIB (IEEE-488) interface option
can be substituted for the RS-232 interface. Please refer to the Option section of this manual
for details on the 7630 options. The RS-232 interface also uses the same command set as the
GPIB interface for setting of test parameters. However there are many functions of the GPIB
488.2 interface that are not available through RS-232. The IEEE-488 interface included with
7630 conforms to the requirements of the IEEE-488.2 standard.
6.2.1 GPIB Messages
There are typically two types of messages that GPIB devices use to communicate with other
interconnected GPIB devices;
Interface messages:
Often called commands or command messages and Device dependent
messages often called data or data messages.
Data Messages:
Contain information such as programming instructions or measurement
results. Command Messages perform functions such as initializing the bus and addressing
and unaddressing devices.
6.2.2 Functions
A GPIB device can be a Listener, Talker and/or Controller. A Talker sends data messages to
one or more Listeners, which receive data. A Controller manages the information flow on
the GPIB by sending commands to all devices. The GPIB bus is much like a computer bus
except a computer has circuit cards connected via a backplane and the GPIB has stand-alone
devices connected via a cable.
6.2.3 Signals and Lines
The GPIB consists of 16 signal lines and 8 ground-return or shield drain lines. The 16 signal
lines are grouped into 8 data lines, 3 handshake lines and 5 interface management lines.
Data Lines: The eight data lines, DI01 through DI08 carry data and command messages.
The 7-bit ASCII or ISO code set is used and the eighth bit DI08 is unused.
Handshake Lines: The transfer of message bytes between devices is done via three
asynchronously control lines. Referred to as three-wire interlocked handshake. This
guarantees that message bytes on the data lines are sent and received without transmission
error.
NRFD
(not ready for data) indicates when a device is ready or not ready to receive a
message byte.