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SECTION 4
GPIB
Interface
D101
D102
D103
D104
EOI
DA"
NRFD
NDAC
IFC
SRQ
ATN
SHIELD
D105
D106
D107
D108
REN
DAV GROUND
NRFD GROUND
NDACGROUND
IFC GROUND
SRQ GROUND
ATN GROUND
LOGIC GROUND
IEEE-488
'igure 4-l.
InterfaceConnector
4.1.3
Bus Line Signals
and Operation
The GPIB bus consists of 24 lines, including
eight data
lines, eight control lines, and eight signal/system
ground
lines.
Data Bus CD101 to DIOS)
DIOl
through
DIOS are the data input/output
lines,
whichareusedtotransferbothaddressandcommandin-
formation
(the type of data present on these lines is deter-
mined by the ATN line). DIOl is the least significant
bit
(LSB).
Handshake
Bus (DAV, NRFD, NDAC)
These three lines are handshake lines used to ensure reli-
able data transfer.
DAV (DAta Yalid)
This line indicates that the data on the DIO lines sent
from a talker or the controller
are valid.
NRFD mot Ready For Data)
This line indicates when listeners are ready to accept data
over the data lines.
NDAC mot Data Xcepted)
This line indicates the acceptance of data by listeners.
cow01
BUS (ATN, REN, IFC, SRQ, EOI)
ATN (eTteNtion)
This line is an output line from the controller, and it indi-
cates whether the information
on the data bus is to be ix-
terpreted as data or commands.
REN @emote ENable)
This output line from the controller
switches devices be-
tween remote control and local control.
This output line from the controller clears the interface of
active talkers and listeners.
This control line is used by a device to request service
from the controller. The contmller
detects this signal and
usually executes a serial or parallel poll operation.
EOI (End Or Identify)
This line is used to indicate the end of a multiple-byte
transfer sequence or, in conjunction
with ATN, to execute
a parallel poll operation.
4.1.4
GPIB Handshaking
GI'IB handshaking
is performed by checking the status of
all the listeners and inhibiting
the next data transfer until
all listeners have completed the reception of data, so that
the slowest device on the bus can perform data transfer
reliably. The handshaking
operations are executed by the
following
handshake line logic levels:
4-2
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