Your IOtech warranty is as stated on the product warranty card. You may contact IOtech by phone,
fax machine, or e-mail in regard to warranty-related issues.
Phone: (440) 439-4091, fax: (440) 439-4093, e-mail:
Limitation of Liability
IOtech, Inc. cannot be held liable for any damages resulting from the use or misuse of this product.
Copyright, Trademark, and Licensing Notice
All IOtech documentation, software, and hardware are copyright with all rights reserved. No part of this product may be
copied, reproduced or transmitted by any mechanical, photographic, electronic, or other method without IOtech’s prior written
consent. IOtech product names are trademarked; other product names, as applicable, are trademarks of their respective
holders. All supplied IOtech software (including miscellaneous support files, drivers, and sample programs) may only be used
on one installation. You may make archival backup copies.
FCC Statement
IOtech devices emit radio frequency energy in levels compliant with Federal Communications Commission rules (Part 15)
for Class A devices. If necessary, refer to the FCC booklet How To Identify and Resolve Radio-TV Interference Problems
(stock # 004-000-00345-4) which is available from the U.S. Government Printing Office, Washington, D.C. 20402.
CE Notice
Many IOtech products carry the CE marker indicating they comply with the safety and emissions standards of the
European Community. As applicable, we ship these products with a Declaration of Conformity stating which
specifications and operating conditions apply.
Warnings, Cautions, Notes, and Tips
Refer all service to qualified personnel. This caution symbol warns of possible personal injury or equipment damage
under noted conditions. Follow all safety standards of professional practice and the recommendations in this manual.
Using this equipment i n ways other than described in t his manual can present serious safety hazards or cause equipment
damage.
sales@iotech.com
This ESD caution symbol urges proper handling of equipment or components sensitive to damage from electrostatic
discharge. Proper handling guidelines include the use of grounded anti-static mats and wrist straps, ESD-protective
bags and cartons, and related procedures.
Specifications and Calibration
Specifications are subject to change without notice. Significant changes will be addressed in an addendum or revision to the
manual. As applicable, IOtech calibrates its hardware to published specifications. Periodic hardware calibration is not
covered under the warranty and must be performed by qualified personnel as specified in this manual. Improper calibration
procedures may void the warranty.
Quality Notice
IOtech has maintained ISO 9001 certification since 1996. Prior to shipment, we thoroughly test our products and
review our documentation to assure the highest quality in all aspects. In a spirit of continuous improvement, IOtech
welcomes your suggestions.
The enclosure of the Isolator488 Bus Isolator is
internally connected to earth ground through the
power cord. However, the shield of the IEEE 488
cables attached to the Isolator488 and signal ground
pins may be at a high voltage with respect to earth
ground. Be sure to remove power from all devices in
your system before handling IEEE 488 cables
connected to the Isolator488. Failure to follow this
warning may result in personal injury or death.
The Isolator488 increases the number of IEEE instruments and devices allowable
on the bus from 15, including the controller, to 28 while also providing optical
isolation between the system controller and devices on the isolated bus. Since the
Isolator488 does not occupy a bus address, its operation is entirely transparent to the
IEEE controller. The IEEE standard defines 31 valid primary bus addresses.
Therefore, no special software or bank switching is necessary to access the additional
devices allowed by the Isolator488. The Isolator488 and has no effect on bus data
transfer rates.
Two IEEE ports are provided. One connects directly to the controller's IEEE bus,
the other to an additional 14 instruments, printers, plotters and specialized peripherals
which may need to be optically isolated from the system controller.
1.2 AVAILABLE ACCESSORIES
Additional accessories that can be ordered for the Isolator488 include:
/ATN to Local Data355 nS typ., 475nS Max.
/ATN to Local DAV155 nS typ., 2075 nS Max.
Data Lines85 nS typ., 120 nS Max.
Command Lines90 nS typ., 125nS Max.
Parallel Poll Response140 nS typ., 205 nS Max.
SIGNAL LINE DIRECTIONS:
Data Lines:
DIO1 - DIO7Bidirectional
Handshake Lines:
DAV, NRFD, NDACBidirectional
Command Lines:
SRQ, ATN, REN, IFCTo Local Bus
ATNTo Remote Bus
EOIBidirectional
CONNECTORS:Two IEEE 488 connectors with metric studs
INDICATORS: LED for Power
POWER: 105-125V or 210-250V,50, 60 Hz; 20 VA MAX.
ENVIRONMENT: 0 to 50 °C; 0 to 70% RH
DIMENSIONS: 425 mm deep x 45 mm wide x 208 mm high.
(16.75 "x 1.75 "x 8.20 ")
WEIGHT: 2.1 kg (4.6 lbs)
CONTROLS: Power switch
SUPPLIED ACCESSORIES:Power cable and manual
ISOLATION: IEEE 488 common on Controller Bus to IEEE 488
common on Instrument Bus:
1600 volts peak maximum @ sea level to 10,000 ft.
0 - 70° C, and 0 - 80% RH non-condensing OR
5
500 Vac maximum, 10
Specifications are subject to change without notice.
V-Hz
1.2
Section 1Introduction
1.4 Abbreviations
The following IEEE 488 abbreviations are used throughout this manual.
addr nIEEE bus address "n"
ATNAttention line
CAController Active
CRCarriage Return
dataData String
DCLDevice Clear
GETGroup Execute Trigger
GTLGo To Local
LAListener Active
LAGListen Address Group
LFLine Feed
LLOLocal Lock Out
MLAMy Listen Address
MTAMy Talk Address
PPCParallel Poll Configure
PPUParallel Poll Unconfigure
SCSystem Controller
SDCSelected Device Clear
SPDSerial Poll Disable
SPESerial Poll Enable
SRQService Request
TATalker Active
TADTalker Address
TCTTake Control
termTerminator
UNLUnlisten
UNTUntalk
*Unasserted
1.3
Section 2Getting Started
GETTING STARTED
2.1 Inspection
The Isolator488 was carefully inspected, mechanically and electrically, prior to
shipment. When you receive the interface, carefully unpack all items from the
shipping carton and check for any obvious signs of physical damage which may have
occurred during shipment. Report any damage to the shipping agent immediately.
Remember to retain all shipping materials in the event that shipment back to the
factory becomes necessary.
Every Isolator488 is shipped with the following....
•
Isolator488
•
123-0900
•
123-0800
2.2 Configuration
Before using the Isolator488, you should be aware of the connections
between the IEEE digital commons, the shield lines on each bus, and earth ground.
The following information is provided so that you can determine if the factory
configuration is appropriate for your application or if some changes need to be
made prior to use.
The following is a list of terms and their definitions as used in this manual:
IsolationThe ability of the Isolator488 to break the electrical
connection between the shields and digital commons
of its IEEE 488 ports while allowing the transfer of
data.
IEEE Bus Isolator
Instruction Manual
Accessory Kit ( includes power cable,
fuse, and rack mounting hardware)
2.1
Section 2Getting Started
Earth GroundThe Ground terminal on the AC power cable. This is
internally connected to the chassis of the Isolator488.
Controller PortThe IEE 488 port labeled CONTROLLER on the rear
panel of the Isolator488. The system controller
must be connected to this port. Instruments may also be
connected to this port, but instruments placed in the
CONTROLLER port will not be isolated from the
system controller.
Instrument PortThe IEEE488 port labeled INSTRUMENTS on the
rear panel of the Isolator488. Instruments may be
connected to this port. Instruments connected to the
Instrument Port may be isolated from devices on the
Controller Port depending on the internal configuration
of the Isolator 488.
Controller Common The logic common connection on the Controller Port.
Pins 18, 19, 20, 21,22, 23, and 24 of the Controller
Port are all connected to Controller Common.
Instrument Common The logic common connection on the Instrument Port.
Pins 18, 19, 20, 21, 22, 23, and 24 of the Controller
Port are all connected to Instrument Common.
Controller Shield The Shield connection (Pin 12) on the Controller Port.
Instrument Shield The Shield connection (Pin 12) on the Instrument Port
The factory configuration of the Isolator488 is as follows:
2.2
Section 2Getting Started
2.3
Section 2Getting Started
As shown in the preceding diagram, the Isolator488 is shipped with a 'soft ground'
consisting of a 1 MΩ resistor in parallel with a 0.01 µF capacitor between local
Common and Earth Ground. This configuration should be suitable for most
applications. If you wish to make any changes to this configuration, follow the
steps given below.
2.3 Modifications
The Isolator488, as shipped from the factory, is configured for the typical use
of the unit which is to isolate the instrument port from Earth ground and from
Controller common. The factory configuration should be used unless you have a
significant variation in your application beyond galvanic isolation devices on the
Instrument port. If the factory configuration is not appropriate for your
application, the following procedures may be undertaken to modify the
Isolator488. It is necessary to open the enclosure to make any of the following
changes. If yoou have any questions about a particular change, please contact the
applications department at (440) 439-4091.
1. Disconnect the power cord from the AC line and from the Isolator488.
Disconnect any IEEE cables prior to disassembly.
WARNING
Never open the Isolator488 case while it
is connected to the AC line. Internal
voltage potentials exist which could
cause personal injury or death.
2.Place the Isolator488 on a flat surface. Remove the six screws on top of the
case and remove the top cover. Located to the right of the Controller Port IEEE
488 connector are locations for C16, R4, and F2. Located to the right of the
Instrument Port IEEE 488 connector are locations for C59, R5, and F3. Refer to
the following figure:
2.4
Section 2Getting Started
C59
R5
F3
C50
Instrument Port
Common Components
C49
JPR2
TO INSTRUMENTS
C47C48
Isolator488 Internal View
C16
R4
F2
Controller Port
Common Components
JPR1
TO CONTROLLER
2.5
Section 2Getting Started
The following options are available on
each
port:
1. The Shield pin of the IEEE 488 connector (pin 12) may be connected to the
logic common of the IEEE 488 connector (pins 18, 19, 20, 21, 22, 23, and 24) or
left unconnected.
2. Logic common of IEEE 488 connector (pins 18, 19, 20, 21, 22, 23, and 24) may
be connected to the chassis of the Isolator488, connected to the chassis through a
soft ground, or left unconnected.
The following changes may be made to the Controller Port:
1. To remove the Controller common from earth ground, remove R4, and C16 by
either desoldering the components (the bottom panel or the Isolator488 must be
removed in order to do this) or cutting the component leads so that they may be
removed. Make note of this change for later reference.
2. To connect Controller common to earth ground, insert a 1/2 amp fuse in the fuse
clips labelled F2. The 1/2 amp fuse connects the Controller common to earth
ground and limits fault currents to 1/2 amp. Make note of this change for later
reference.
3. To connect pin 12 (shield) of the Controller Port to Controller Common, solder
a jumper wire in the location labeled JPR1. Make note of this change for later
reference.
The following changes may be made to the Instrument Port:
1. To add a soft ground between the Instrument Common and earth ground, insert
a 1 MΩ 1/4 watt resistor in the location labelled R5. Insert a 0.01 µF 2kv ceramic
capacitor in the location labelled C59. Solder these components in place from the
solder side of the circuit board using rosin core solder. The bottom panel or the
Isolator488 will need to be removed in order to do this. Make note of these
changes for later reference.
2.6
Section 2Getting Started
2. To connect the Instrument Common to earth ground, insert a 1/2 amp fuse in the
fuse clips labelled F3. Make note of this change for later reference.
3. To connect pin 12 (shield) of the Instrument Port to Instrument Common, solder
a bare jumper wire in the location labeled JPR2. Make note of this change for later
reference.
After making any changes to the Isolator488 internal circuitry, be sure to
document your changes then carefully reassemble the unit.
2.4Line Voltage Selection
The Isolator 488 is designed to accept either 105 to 125 volt or 210 to 250
volt, 50 or 60 Hz, AC power. Each unit, when shipped from the factory, is labeled
with its input voltage setting. If this setting is not appropriate, the internal voltage
selection witch must be changed. Failure to operate the Isolator488 from
appropriate power source may result in damage to the unit. To check or change the
voltage selection switch disconnect all cables from the Isolator488 and follow the
steps below.
Isolator Fuse and Line Voltage Switch Locations
WARNING :
S2
F1
Power Connector
115V
LETHAL VOLTAGES
MAY BE PRESENT
S1
2.7
Section 2Getting Started
WARNING
Never open the Isolator488 case while it
is connected to the AC line. Internal
voltage potentials exist which could
cause personal injury or death.
1.Place the Isolator488 on a flat surface. Remove the six screws on top of the
case and remove the top cover. Located next to the rear panel power connector is
switch S2 and fuse F1.
2.Insert the tip of a small screwdriver into the slot of the switch and move the
switch to the left or right so that the desired line voltage selection appears on the
switch. Make note of the new setting for later reference.
CAUTION
Use the 1/2 amp fuse, FU-1-.5, for 115
volt operation. Use the 1/4 amp fuse,
FU-1-.25, for 230 volt operation. Failure
to use the correct fuse could result in
damage to the Isolator488.
3.Replace the 1/2 amp fuse, FU-1-.5 (for 115 volt operation), with the 1/4 Amp
fuse (for 230 volt operation), part number FU-1-.25, that is included in the
Isolator488 Accessory Kit.
4.Carefully reassemble the unit.
WARNING
The Isolator488 is intended for INDOOR
USE ONLY. Failure to observe this
warning could result in equipment
failure, personal injury or death.
2.8
Section 2Getting Started
2.5 Hardware Installation
Included with the Isolator488 Bus Isolator are accessories for rack or bench
use. If rack mount installation is required, install the two rack ears using the
enclosed screws. These ears can be installed so either the front or the rear of the
unit faces the front of the rack fixture.
View of Enclosure showing Rack Hardware Installation
Enclosure
Enclosure
Top or Bottom View
Rack Ear
Screw
(2 per ear)
If bench installation is required, the rubber feet can be installed on the
underside of the unit near each corner.
View of Enclosure Bottom Showing Feet Placement
Enclosure
Top View
Enclosure
Bottom View
Top View
2.9
Section 2Getting Started
2.6 Operation
To begin operating the Isolator488, plug the power supply into the rear panel
jack. Apply power to the Isolator488 by depressing the rear panel power switch.
The front panel POWER LED should turn on.
If the POWER indicator does not light, there may not be any power supplied to
the interface. In this event, check to make sure the AC power is supplied to the
Isolator488, and that the power cord is properly installed into the unit. If the problem
is unresolved, refer to the Service Information section (Section 4) of this manual.
If proper operation is obtained, turn off the Isolator488 and connect the other
IEEE 488 devices to each of the Isolator488 ports. Apply power to all devices in the
system.
Once all IEEE devices have been connected and powered on, the Isolator488 will
allow the system co ntroller to command up to 13 IEEE dev ices on its Controller Po rt
(in addition to itself and the Isolator488), and up to 14 IEEE devices on the Instrument
Port. The Isolator488 has no address of its own, and therefore will operate completely
transparent to the system. Be careful not to have two IEEE devices with the same
address connected to either ports. Failure to do so will result in the bus 'locking up'
when one of the devices is accessed.
2.6.1 Bus Loading
The IEEE 488 specification allows for a maximum of 15 bus loads.
The Isolator488 presents one bus load on each port. Therefore, an
additional 14 devices can be placed on each the CONTROLLER and
INSTRUMENT ports. Because the IEEE co ntroller pres ents one b us load,
a total of 27 instruments, printers, plotters and other peripherals can be
accessed from a single IEEE controller.
2.10
Section 2Getting Started
2.6.2 Cabling Length
The IEEE 488 specification allows for cabling distance between bus
devices of 2 meters (approx. 7 feet). The total worst case distance from the
two furthest devices is not allowed to exceed 20 meters (approx. 70 feet).
The addition of the Isolator488 does not increase this distance.
SRQTo Controller Bus
ATNTo Instrument Bus
EOIBidirectional
RENTo Instrument Bus
IFCTo Instrument Bus
The majority of the command lines have their signal direction fixed.
This forces bus control from the CONTROLLER bus.
When Attention (ATN) is asserted, the data lines, talker handshake
line (DAV) and the EOI line direction is forced from the CONTROLLER
to the INSTRUMENT port. The listener handshake lines (NRFD and
NDAC) are forced from the INSTRUMENT to the CONTROLLER port.
The commands are sent through the Isolator488 to the INSTRUMENT
port.
2.11
Section 2Getting Started
When ATN is unasserted, the Isolator488 asserts NDAC on both ports,
for a minimum of 200 nanoseconds, while looking for an active talker. If
the talker is detected on the CONTROLLER port, the NDAC lines are
released and the data and handshake line directions remain unchanged. If
the active talker is detected on the INSTRUMENT port, the data line
direction is force to the CONTROLLER port and the handshake line
directions are reversed. The Isolator488 delays a minimum of 1200
nanoseconds to allow the data lines to settle before releasing the NDAC
lines. Once changed, data transfers to 1 megabyte per second are possible.
2.6.4 Parallel Polling
During data transfer operations, the data line transceivers are operated
in tri-state. When a parallel poll is detected, the CONTROLLER port
transceiver is changed to open-collector and the data line direction is forced
from the Instrument Port to the Controller Port. Parallel polling
propagation delay through the Isolator488 is typically 85 nanoseconds.
2.6.5 Passing Control
If another device is included in the system which can receive control,
it must be placed on the CONTROLLER port. IEEE 488 control can not be
passed through the Isolator488.
2.12
Section 3IEEE 488 Primer
IEEE 488 Primer
3.1 HISTORY
The
IEEE 488
bus is an instrumentation co mmunication bus adopted
by the Institute of Electrical and Electronic Engineers in 1975 and revised in
1978. The
Isolator488
IEEE 488-1978
.
conforms to this most recent revision designated
Prior to the adoption of this standard, most instrumentation
manufacturers offered their own versions of computer interfaces. This
placed the burden of system hardware design on the end user. If his
application required t he products of several different manufacturers , then he
might need to design several different hardware and software interfaces.
The popularity of the
urpose Interface Bus or
P
IEEE 488
GPIB
interface (sometimes called the General
) is due to the total specification of the
electrical and mechanical interface as well as the data transfer and control
protocols. The use of the
IEEE 488
standard has moved the responsibility of
the user from design of the int erface to d esign of th e high level soft ware that
is specific to the measureme nt appl ica ti on.
3.2 GENERAL STRUCTURE
The main purpose of the
GPIB
is to transfer information bet ween two
or more devices. A device can either be an instrument or a computer.
Before any information transfer can take place, it is first necessary to specify
which will do the talking (send data) and which devices will be allowed to
listen (receive data). The decision of who will talk and who will listen
usually falls on the
Controller
The
.
System Controller
System Controller
is similar to a committee chairman. On a well
which is, at power on, the
Active
run committee, only one person may speak at a time and the chairman is
responsible for recognizing members and allowing them to have their say.
On the bus, the device which is recognized to speak is the
Active Talker
There can only be one Talker at a time if the information transferred is to be
clearly understood by all. The act of "giving the floor" to that device is
called
Addressing to Talk
. If the committee chairman can not attend the
meeting, or if other matters require his attention, he can appoint an acting
chairman to take control of the proceedings. For the
becomes the
Active Controller
.
GPIB
, this device
.
3-1
Section 3IEEE 488 Primer
At a committee meeting, everyone present usually listens. This is not
the case with the
GPIB
. The
Active Controller
selects which devices will
listen and commands all other devices to ignore what is being transmitted. A
device is instructed to listen by being
then referred to as an
message are instructed to
Active Listener
Unlisten
Addressed to Listen
. This device is
. Devices which are to ignore the data
.
The reason some devices are instructed to
Unlisten
is quite simple.
Suppose a college instructor is presenting the day's lesson. Each student is
told to raise their hand if the inst ructor has exceed ed their ability to keep up
while taking notes. If a hand is raised, the inst ructor stops his discussio n to
allow the slower students the time to catch up. In this way, the instructor is
certain that each and every student receives all the information he is trying to
present. Since there are a lot of students in the classroom, this exchange of
information can be very slow. In fact, the rate of information transfer is no
faster than the rate at which the slowest note-taker can keep up. The
instructor, though, may have a message for one particular student. The
instructor tells the rest of the class to ignore this message (
Unlisten
) and
tells it to that one student at a rate which he can understand. This
information transfer can then happen much quicker, because it need not wait
for the slowest student.
GPIB
The
transfer is called
For data transfer on the
transfers information in a similar way. This method of data
handshaking
. More on this later.
IEEE 488
Active Controller
, the
must …
a)
b)D esignate who wil l
c)Designate all the devices who are to
devices to
Unlisten
all devices to protect against eavesdroppers.
listen
talk
.
addressing
by
a device to
listen
by
addressing
d)Indica te to all de vices that the da ta transfer can ta ke place.
3-2
talk
.
those
Section 3IEEE 488 Primer
}
D
DAVN
N
IFCA
SRQR
EOIT
D
D
D
a
D
P
D
D
D
T
C
G
I
M
o Other Devices
evice 1
System Controller
Able to Talk,
Listen, and Control
ata Bus
evice 2
MM
Able to Talk
nd Listen
evice 3
rinter
Only Able to Listen
ata Byte
ransfer
ontrol
eneral
nterface
anagement
evice 4
Frequency Counter
Only Able to Talk
IEEE 488 Bus Structure
Figure 3.1
IO1-8
RFD
DAC
TN
EN
3-3
Section 3IEEE 488 Primer
3.3 SEND IT TO MY ADDRESS
In the previous discussion, the terms
Addressed to Listen
IEEE 488
The
were used. These terms require some clarification.
standard permits up to 15 devices to be configured
Addressed to Talk
and
within one system. Each of these devices must have a unique address to
avoid confusion. In a similar fashion, every building in town has a unique
address to prevent one home from receiving another home's mail. Exactly
how each device's address is set is specific to the product's manufacturer.
Some are set by DIP switches in hardware, oth ers by software. Consult the
manufacturer's instructions to determine how to set the address.
Addresses are sent with
Active Controller
My Talk Address
Address Group
. These commands include
(MTA),
(LAG).
universal (multiline
My Listen Address
Talk Address Group
) commands from the
(MLA),
(TAG), and
Listen
3.4 BUS MANAGEMENT LINES
Five hardware lines on the
Signals on these lines are often referred to as
GPIB
are used for bus management.
uniline
(single line)
commands. The signals are active low, i.e. a low voltage represents a logic
"1" (asserted), and a high voltage represents a logic "0" (unasserte d).
3.4.1 Attention (ATN)
ATN
is one of the most important lines for bus management. If
Attention is asserted, then the information contained on the data lines is
to be interpreted as a multiline command. If it is not, then that
information is to be interpreted as data for the
Active Controller
is the only bus device that has control of this line.
3-4
Active Listener
s. The
Section 3IEEE 488 Primer
3.4.2 Interface Cle ar (IFC)
The
IFC
line is used only by the
System Controller
. It is used to
place all bus devices in a known state. Although device configurations
vary, the
Listen Idle states (neither
IFC
command usually places the devices in the Talk and
Active Talker
Active Listener
nor
).
3.4.3 Remote Enable (REN)
When the
System Controller
sends the
devices will respond to remote operation. Generally, the
REN
command, bus
REN
command
should be issued before any bus programming is attempted. Only the
System Controller
has control of the
Remote Enable
line.
3.4.4 End or Identify (EOI)
EOI
The
transfer. The device that is sending the data asserts
transfer of the last data byte. The
line is used to signal the last byte of a multibyte data
EOI
during the
EOI
signal is not always necessary as
the end of the data may be indicated by some special character such as
carriage return.
Active Controller
The
simultaneously asserting
also uses
EOI
and
EOI
ATN
to perform a
.
Parallel Poll
by
3.4.5 Service Request (SRQ)
When a device desires the immediate attention of the
Controller
it asserts
SRQ
. It is then the Controller's responsibility to
Active
determine which device requested service. This is accomplished with a
Serial Poll
Parallel Poll
or a
.
3-5
Section 3IEEE 488 Primer
3.5 HANDSHAKE LINES
GPIB
The
uses three handshake lines in an "I'm ready - Here's the data
- I've got it" sequence. This handshake protocol assures reliable data
transfer, at the rate determined by the slowest Listener. One line is
controlled by the Talker, while the other two are shared by all Active
Listeners. The handshake lines, like the other
IEEE 488
lines, are active
low.
3.5.1 Data Valid (DAV)
DAV
The
NDAC
is asserted (active low) which indicates that all Listeners have
line is controlled by the
accepted the previous data byte transferred. The
data on the bus and waits until
Talker
NRFD
. The
Talker
Talker
verifies that
then outputs
is unasserted (high) which
indicates that all Addressed Listeners are ready to accept the
information. When
asserts
DAV
( active low) to indicate that the da ta on the bus is va lid.
NRFD
and
NDAC
are in the proper state, the
Talker
3.5.2 Not Ready for Data (NRFD)
This line i s used by t he
Listeners
are ready to accept new data. The
to inform the
Talker
must wait for each
Talker
when they
Listener
to unassert this line (high) which they will do at their own rate when
they are ready for more data. This assures that all devices that are to
accept the information are ready to receive it.
3.5.3 Not Data Accepted (NDAC)
NDAC
The
indicates to the
line is also controlled by the
Talker
that each device addressed to listen has accepted
the information. Each device releases
NDAC
the
will not go high until the slowest Listener has accepted the
NDAC
Listeners
. This line
(high) at its own rate, but
data byte.
3-6
Section 3IEEE 488 Primer
1st Data Byte2nd Data Byte
DIO1-8
(composite)
DAV
Source
ValidNot
Valid
Valid
Not
Valid
NRFD
Acceptor
NDAC
Acceptor
All
Ready
None
Accept
None
Ready
Accept
All
All
Ready
None
Accept
None
Ready
All
Accept
IEEE Bus Handshaking
3.6 DATA LINES
GPIB
The
transfer. These eight data lines use the convention of
provides eight data lines for a bit parallel/byte serial data
DIO1
through
DIO8
instead of the binary designation of D0 to D7. The data lines are
bidirectional a nd are active low.
3.7 MULTILINE COMMANDS
Multiline
(bus) commands are sent by the
data bus with
ATN
asserted. These commands include addressing
Active Controller
over the
commands for talk, listen, Untalk and Unlisten.
3.7.1 Go To Local (GTL)
This command allows the selected devices to be manually
controlled. ($01)
3-7
Section 3IEEE 488 Primer
3.7.2 Listen Address Group (LAG)
There are 31 (0 to 30) listen addresses associated with this group.
The 3 most significant bits of the data bus are set to 001 while the 5 least
significant bit s are the ad dre ss of the device be in g told to li st en.
3.7.3 Unlisten (UNL)
This command tells all bus devices to Unlisten. The same as
Unaddressed to Listen. ($3F)
3.7.4 Talk Address Group (TAG)
There are 31 (0 to 30) talk addresses associated with this group.
The 3 most significant bits of the data bus are set to 010 while the 5 least
significant bit s are the addre ss of the dev ice be ing to ld to talk.
3.7.5 Untalk (UN T)
This command tells bus devices to Untalk. The same as
Unaddressed to T alk. ($5F)
3.7.6 Local Lockout (LLO)
Issuing the
LLO
command prevents manual control of the
instrument's f unctions. ($ 11)
3.7.7 Device Clear (DCL)
This command causes all bus devices to be initialized to a predefined or power u p state. ($14)
3-8
Section 3IEEE 488 Primer
3.7.8 Selected Device Clear (SDC)
This causes a single device to be initialized to a pre-defined or
power up state. ($04)
3.7.9 Serial Poll Disable (SPD)
SPD
The
command disables all devices from sending their Serial
Poll status byte. ($19)
3.7.10 Serial Poll Enable (SPE)
A device which is Addressed to Talk will output its Serial Poll
status byte after
SPE
is sent and
ATN
is unasserted. ($18)
3.7.11 Group Exec ute Trigger (GET)
This command usually signals a group of devices to begin
executing a triggered action. This allows actions of different devices to
begin simul taneously. ($08)
3.7.12 Take Control (TCT)
This command passe s bus control responsibil ities from the current
Controller
to another de vice which has the ability to control. ($09)
3.7.13 Secondary Command Group (SCG)
These are any one of the 32 possible commands (0 to 31) in this
group. They must im mediately follow a talk or listen address. ($60 to
$7F)
3-9
Section 3IEEE 488 Primer
3.7.14 Parallel P oll Configure (PPC)
This configures devices capable of performing a
which data bit t hey are to assert in response to a
Parallel Poll
Parallel Poll
as to
. ($05)
3.7.15 Parallel Poll Unconfigure (PPU)
This disables all devices from responding to a
Parallel Poll
. ($15)
3.8 MORE ON SERVICE REQUESTS
Most of the commands covered, both uniline and multiline, are the
responsibility of the
Active Controller
to send and the bus devices to
recognize. Most of these happen routinely by the interface and are totally
transparent to the system programmer. Other commands are used directly
by the user to provide optimum system control. Of the uniline commands,
SRQ
is very important to the test system and th e software designer h as easy
access to this line by most devices. Service Request is the method by which
a bus device can signal to the
Controller
that an even t has occurred . It is
similar to an interrupt in a microprocessor ba sed system.
Most intelligent bus peripherals have the ability to assert
SRQ
. A
DMM might assert it when its measurement is complete, if its input is
overloaded or for any of an assortment of reasons. A power supply might
SRQ
if its output has current limited. This is a powerful bus feature that
removes the burden from the
"Are you done yet?". Instead, the
System Controller
Controller
says, "Do what I told you to
to periodically inquire,
do and let me know when you're done" or "Tell me when something is
wrong."
Since
Controller
SRQ
is a single line command, there is no way for the
to determine which device requested the service without
additional information. This information is provided by the multiline
commands for
Serial Poll
Parallel Poll
and
.
3-10
Section 3IEEE 488 Primer
3.8.1 Serial Poll
Suppose the
Controller
receives a service request. For this
example, let's assume there are several devices which could assert
SRQ
. The
Controller
issues an
SPE
(Serial Poll enable) command to
each device sequentially. If any device responds with DIO7 asserted it
indicates to the
Controller
that it was the device that asserted
SRQ
Often times the other bits will indicate why the device wanted service.
Serial Polling
This
sequence, and any resulting action, is under control
of the software designer.
3.8.2 Parallel Poll
Parallel Poll
The
is another way the
Controller
can determine
which device requested service. It provides the who but not
necessarily the why. When bus devices are configured for Parallel Poll,
they are assigned one bit on the data bus for their res ponse. By using
the Status bit, the logic level of the response can be programmed to
allow logical OR/AND condit ions on one data line by more t han one
device. When
conducts a
Parallel Poll
SRQ
is asserted , the
. The
Controller
Controller
(under user's software)
must then analyze the eight
bits of data received to determine the source of the request. Once the
source is determined, a
Serial Poll
might be used to determine the
why.
.
Of the two polling ty pes, the
Serial Poll
is the most po pular due to i ts
ability to determine the who and why. In addition, most devices support
Serial Poll
only.
3-11
Service Information
4.1 FACTORY SERVICE
IOtech
encountered in using the Expander488 you should first telephone the factory. Many
problems can be resolved by discussing the problems with our applications
department. If the problem cannot be solved by this method, you will be instructed as
to the proper return procedure.
maintains a factory service center in Cleveland, Ohio. If problems are
Appendix ACharacter Codes And IEEE Multiline Messages
E
FSG
R
U
0
1
2
345
6
7
89:
;
<
=>?
@
A
B
CDE
F
G
HIJ
K
L
MNO
P
Q
R
STU
V
W
XYZ
[
\
]^_
`
a
b
cde
f
g
hij
k
l
mno
$30$40$50$
$31$41$51$
$32$42$52$
$33$43$53$
$34$44$54$
$35$45$55$
$36$46$56$
$37$47$57$
$38$48$58$
$39$49$59$
$3A$4A$5A$
$3B$4B$5B$
$3C$4C$5C$
$3D$4D$5D$
$3E$4E$5E$
$3F$4F$5F$
1
17181
2
2
2
232425262
2
2
30U
0
01020
0
0
0
070809101
1
1
141
1
17181
2
2
2
232425262
2
2
30U
S
SCGSCGS
S
S
S
SCGSCGSCGSCGS
S
S
SCGS
4864809
495
5
525
5
656
6
686
7
818
8
848
8
979
9
1001
1
555
5
585
6
717
7
747
7
878
8
909
9
1031
1
1061
1
6162637778799394951091101
TAGS
T
S
$00$10$20
$01$11$21
GTLLLO
$02$12$22
$03$13$23
$04$14$24
SDCDCL
$05$15$25
PPCPPU
$06$16$26
$07$17$27
$08$18$28
GETSPE
$09$19$29
TCTSPD
$0A$1A$2A
$0B$1B$2B
$0C$1C$2C
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
HT
LF
VT
10
11
12
0
1
2
3
4
5
6
7
8
9
16
DLE
00
17
DC1
01
18
DC2
02
19
DC3
03
20
DC4
04
21
NAK
05
22
SYN
06
23
ETB
07
24
CAN
08
25
M
09
26
SUB
10
27
ESC
11
28
FF
12
$0D$1D$2D
$0E$1E$2E
$0F$1F$2F
CR
SO
SI
13
14
15
29
S
13
30
S
14
31
S
15
ACGUCG
SP
#
$
%
&
*
+
!
"
'
(
)
,
-
.
/
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
LAG
6
9
0
1
2
7
8
9
NL
60$70
6112
p
0
6
CG
61$71
SCG
113
q
SCG
0
6
62$72
2
8
114
r
SCG
1
7
63$73
3
9
115
s
3
9
CG
64$74
SCG
116
t
4
3
0
9
CG
65$75
5
01
SCG
117
u
5
4
1
0
CG
66$76
6
02
SCG
118
v
6
2
CG
67$77
SCG
119
w
SCG
6
2
68$78
8
04
120
x
SCG
7
3
69$79
9
05
121
y
SCG
6A$7A
122
z
SCG
9
5
6B$7B
1
07
123
{
1
0
7
6
CG
6C$7C
2
08
SCG
124
|
2
8
CG
6D$7D
SCG
125
}
3
9
CG
6E$7E
SCG
126
~
SCG
6F$7F
11
127
DEL
5
NT
CG
SCG
CG
ACG = Addressed Command Group
UCG = Universal Command Group
LAG = Listen Address Group
AG = Talk Address Group
CG = Secondary Command Group
A.1
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