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The IEC-625 standard uses 25 pin D type connector as the standard and the signal
assignment is:
DATA
Lines Pin No.
----------------------------------
DIO1
1
DI02
2
DI03
3
DI04
4
DI05
14
DI06
15
DI07
16
DI08
17
The active controller manages all bus communications. The state of the ATN line,
driven by the controller, determines whether the data on the data lines will be
interpreted as a bus command or received by other devices as data. When ATN is true,
the IEEE-488 bus is in COMMAND mode. Otherwise, the bus is in DATA mode. In
COMMAND mode the controller is active and all other devices are waiting for
instructions. COMMAND mode instructions which can be issued by the controller
include:
1) Talk Address. A byte transmitted by the controller enables a specified device to
talk. Only one device can be the talker at a time. When a new talker is assigned, the
old one is disabled.
2) Listen Address. A byte transmitted by the controller enables a specified device to
listen. The IEEE-488 bus allows multiple listeners. When new listeners are assigned,
the old listeners are still active.
3) Universal Commands. All devices on the bus will respond to these commands
whether they are addressed or not.
4) Address Commands. These commands are recognized only by the devices that are
addressed as listeners. A few commands are recognized only by the talker.
5) Unaddress Commands. ASCII "?" unaddresses all listeners that have been previ-
ously addressed to listen. This command is called "Unlisten" (UNL). ASCII " "
unaddresses any talker that has been previously addressed to talk. This command is
called "Untalk" (UNT).
MANAGEMENT Lines
-------------------------------------------------
IFC
REN
ATN
SRQ
EOI
HANDSHAKE Lines
-------------------------------------------------
DAV
NRFD
NDAC
CHAPTER 9
Pin No.
10
5
12
11
6
Pin No.
7
8
9
BUS TUTORIAL
67
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