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R E M O T E O P E R A T I O N
Basic GPIB Concepts
38
LDC-3700 Series
C H A P T E R
3
If there is more than one controller, only one can be the Controller In Charge (CIC). Control can be
passed from one controller to another. In a multiple controller system, there can be one "System
Controller’\" capable of asserting control (becoming CIC).
GPIB Cable Connections
Standard GPIB connectors can be connected together (stacked), allowing you to configure the
system linearly, or in a star configuration.
Figure 3.1
GPIB Cable Connections
The GPIB Connector
The standard GPIB connector consists of 16 signal lines in a 24−pin stackable connector. The extra
pins are used for some twisted−pair wires. There are eight data input/output (IO) lines, three
handshake lines, and five interface management lines.
Eight data input/output (DIO) lines carry both data (including device dependent commands) and
interface messages. The ATN interface management line determines whether these lines contain
data or interface messages.
Three handshake lines ensure that all data and messages are reliably transferred:
•
NRFD (not ready for data) indicates whether a device can receive the next byte of data or
message.
•
NDAC (not data accepted) indicates whether a receiving device has accepted a byte of data
or message.
•
DAV (data valid) indicates that the signal levels on the data lines are stable and available for
the receiving device(s) to accept.
Five interface management lines control the flow of information:
•
ATN (attention) is set by the controller in charge to define the I/O lines for data or interface
messages.
•
IFC (interface clear) is set by the system controller to initialize the bus and assert itself as
controller in charge.
•
REN (remote enable) is set by the controller to place addressed devices into remote or local
(front panel) control mode.
Device A
Device B
Device C
Device D
Device A
Device B
Device C
Device D
linear configuration
star configuration
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