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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 device−dependent
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.
• SRQ (service request) can be set by any device in the system to request service from the
controller.
• EOI (end or identify) is used by talkers to identify the end of a message.
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DIO1
DIO2
DIO3
1
13
2
14
DIO4
3
15
EOI
4
16
5
17
DAV
6
18
NRFD
7
19
8
20
NDAC
9
21
IFC
10
22
11
23
SRQ
12
24
ATN
SHIELD
Figure 3.2 GPIB Connector Diagram
R E M O T E O P E R A T I O N
Basic GPIB Concepts
DIO5
DIO6
DIO7
DIO8
REN
GND (Twisted pair with DAV)
GND (Twisted pair with NRFD)
GND (Twisted pair with NDAC)
GND (Twisted pair with IFC)
GND (Twisted pair with SRQ)
GND (Twisted pair with ATN)
SIGNAL GROUND
3
C H A P T E R
19
MPS-8033
!
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