Keithley Instruments, Inc. warrants that, for a period of one (1) year from the date of shipment (3 years for Models 2000,
2001, 2002, 2010 and 2700), the Keithley Hardware product will be free from defects in materials or workmanship. This
warranty will be honored provided the defect has not been caused by use of the Keithley Hardware not in accordance with
the instructions for the product. This warranty shall be null and void upon: (1) any modification of Keithley Hardware that
is made by other than Keithley and not approved in writing by Keithley or (2) operation of the Keithley Hardware outside
of the environmental specifications therefore.
Upon receiving notification of a defect in the Keithley Hardware during the warranty period, Keithley will, at its option,
either repair or replace such Keithley Hardware. During the first ninety days of the warranty period, Keithley will, at its
option, supply the necessary on site labor to return the product to the condition prior to the notification of a defect. Failure
to notify Keithley of a defect during the warranty shall relieve Keithley of its obligations and liabilities under this
warranty.
Other Hardware
The portion of the product that is not manufactured by Keithley (Other Hardware) shall not be covered by this warranty,
and Keithley shall have no duty of obligation to enforce any manufacturers' warranties on behalf of the customer. On those
other manufacturers’ products that Keithley purchases for resale, Keithley shall have no duty of obligation to enforce any
manufacturers’ warranties on behalf of the customer.
Software
Keithley warrants that for a period of one (1) year from date of shipment, the Keithley produced portion of the software or
firmware (Keithley Software) will conform in all material respects with the published specifications provided such Keithley
Software is used on the product for which it is intended and otherwise in accordance with the instructions therefore.
Keithley does not warrant that operation of the Keithley Software will be uninterrupted or error-free and/or that the Keithley
Software will be adequate for the customer's intended application and/or use. This warranty shall be null and void upon any
modification of the Keithley Software that is made by other than Keithley and not approved in writing by Keithley.
If Keithley receives notification of a Keithley Software nonconformity that is covered by this warranty during the warranty
period, Keithley will review the conditions described in such notice. Such notice must state the published specification(s)
to which the Keithley Software fails to conform and the manner in which the Keithley Software fails to conform to such
published specification(s) with sufficient specificity to permit Keithley to correct such nonconformity. If Keithley determines that the Keithley Software does not conform with the published specifications, Keithley will, at its option, provide
either the programming services necessary to correct such nonconformity or develop a program change to bypass such
nonconformity in the Keithley Software. Failure to notify Keithley of a nonconformity during the warranty shall relieve
Keithley of its obligations and liabilities under this warranty.
Other Software
OEM software that is not produced by Keithley (Other Software) shall not be covered by this warranty, and Keithley shall
have no duty or obligation to enforce any OEM's warranties on behalf of the customer.
Other Items
Keithley warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries, diskettes,
and documentation.
Items not Covered under Warranty
This warranty does not apply to fuses, non-rechargeable batteries, damage from battery leakage, or problems arising from
normal wear or failure to follow instructions.
Limitation of Warranty
This warranty does not apply to defects resulting from product modification made by Purchaser without Keithley's express
written consent, or by misuse of any product or part.
EXCEPT FOR THE EXPRESS WARRANTIES ABOVE KEITHLEY DISCLAIMS ALL OTHER WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION, ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. KEITHLEY DISCLAIMS ALL WARRANTIES WITH
RESPECT TO THE OTHER HARDWARE AND OTHER SOFTWARE.
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KEITHLEY INSTRUMENTS SHALL IN NO EVENT, REGARDLESS OF CAUSE, ASSUME RESPONSIBILITY FOR
OR BE LIABLE FOR: (1) ECONOMICAL, INCIDENTAL, CONSEQUENTIAL, INDIRECT, SPECIAL, PUNITIVE OR
EXEMPLARY DAMAGES, WHETHER CLAIMED UNDER CONTRACT, TORT OR ANY OTHER LEGAL THEORY,
(2) LOSS OF OR DAMAGE TO THE CUSTOMER'S DATA OR PROGRAMMING, OR (3) PENALTIES OR PENALTY
CLAUSES OF ANY DESCRIPTION OR INDEMNIFICATION OF THE CUSTOMER OR OTHERS FOR COSTS, DAMAGES, OR EXPENSES RELATED TO THE GOODS OR SERVICES PROVIDED UNDER THIS WARRANTY.
The following safety precautions should be observed before using this product and any associated instrumentation.
Although some instruments and accessories would normally be used with non-hazardous voltages, there are situations
where hazardous conditions may be present.
This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety
precautions required to avoid possible injury. Read and follow all installation, operation, and maintenance information
carefully before using the product. Refer to the manual for complete product specifications.
If the product is used in a manner not specified, the protection provided by the product may be impaired.
The types of product users are:
Responsible body is the individual or group responsible for the use and maintenance of equipment, for ensuring that
the equipment is operated within its specifications and operating limits, and for ensuring that operators are adequately
trained.
Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use
of the instrument. They must be protected from electric shock and contact with hazardous live circuits.
Maintenance personnel perform routine procedures on the product to keep it operating properly, for example, setting
the line voltage or replacing consumable materials. Maintenance procedures are described in the manual. The procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.
Service personnel are trained to work on live circuits, and perform safe installations and repairs of products. Only
properly trained service personnel may perform installation and service procedures.
Keithley products are designed for use with electrical signals that are rated Installation Category I and Installation
Category II, as described in the International Electrotechnical Commission (IEC) Standard IEC 60664. Most measurement, control, and data I/O signals are Installation Category I and must not be directly connected to mains voltage
or to voltage sources with high transient over-voltages. Installation Category II connections require protection for high
transient over-voltages often associated with local AC mains connections. Assume all measurement, control, and data
I/O connections are for connection to Category I sources unless otherwise marked or described in the Manual.
Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or
test fixtures. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels
greater than 30V RMS, 42.4V peak, or 60VDC are present. A good safety practice is to expect that hazardous volt-
age is present in any unknown circuit before measuring.
Operators of this product must be protected from electric shock at all times. The responsible body must ensure that
operators are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential human contact. Product operators in these circumstances must be trained to protect themselves from
the risk of electric shock. If the circuit is capable of operating at or above 1000 volts, no conductive part of the circuit
may be exposed.
Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance
limited sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards,
install protective devices to limit fault current and voltage to the card.
Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect
the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.
When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main
input power disconnect device must be provided, in close proximity to the equipment and within easy reach of the
operator.
For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting
or disconnecting cables or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.
Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth)
ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the
voltage being measured.
The instrument and accessories must be used in accordance with its specifications and operating instructions or the
safety of the equipment may be impaired.
Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications and operating information, and as shown on the instrument or test fixture panels, or switching card.
When fuses are used in a product, replace with same type and rating for continued protection against fire hazard.
Chassis connections must only be used as shield connections for measuring circuits, NOT as safety earth ground con-
nections.
If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation re-
quires the use of a lid interlock.
If or is present, connect it to safety earth ground using the wire recommended in the user documentation.
The symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.
The symbol on an instrument shows that it can source or measure 1000 volts or more, including the combined
effect of normal and common mode voltages. Use standard safety precautions to avoid personal contact with these
voltages.
The WARNING heading in a manual explains dangers that might result in personal injury or death. Always read the
associated information very carefully before performing the indicated procedure.
The CAUTION heading in a manual explains hazards that could damage the instrument. Such damage may invalidate
the warranty.
Instrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and all test cables.
To maintain protection from electric shock and fire, replacement components in mains circuits, including the power
transformer, test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses, with applicable
national safety approvals, may be used if the rating and type are the same. Other components that are not safety related
may be purchased from other suppliers as long as they are equivalent to the original component. (Note that selected parts
should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you
are unsure about the applicability of a replacement component, call a Keithley Instruments office for information.
To clean an instrument, use a damp cloth or mild, water based cleaner. Clean the exterior of the instrument only. Do
not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that consist
of a circuit board with no case or chassis (e.g., data acquisition board for installation into a computer) should never
require cleaning if handled according to instructions. If the board becomes contaminated and operation is affected,
the board should be returned to the factory for proper cleaning/servicing.
The information contained in this manual is believed to be accurate and reliable. However, the
manufacturer assumes no responsibility for its use; nor for any infringements of patents or other rights
of third parties that may result from its use. No license is granted by implication or otherwise under any
patent rights of the manufacturer.
THE MANUFACTURER SHALL NOT BE LIABLE FOR ANY SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMA GES RELATED TO THE USE OF THIS PR ODUCT. THIS PRODUCT IS
NOT DESIGNED WITH COMPONENTS OF A LEVEL OF RELIABILITY THAT IS SUITED FOR
USE IN LIFE SUPPORT OR CRITICAL APPLICATIONS.
DriverLINX, SSTNET, and LabOBJX are registered trademarks and DriverLINX/VB is a trademark of
Scientific Software Tools, Inc.
Microsoft and Windows are registered trademarks and Visual C++ and Visual Basic are trademarks of
Microsoft Corporation.
Borland is a registered trademark and Borland C++, Delphi, and Turbo Pascal are trademarks of
Borland International, Inc.
IBM is a registered trademark of International Business Machines Corporation.
Acrobat is a registered trademark of Adobe Systems Incorporated.
All other brand and product names are trademarks or registered trademarks of their respective
companies.
All rights reserved. Reproduction or adaptation of any part of this documentation beyond that permitted
by Section 117 of the 1979 United States Copyright Act without permission of the Copyright owner is
unlawful.
The DDA-08/16 User’s Guide provides the information needed to set up,
install, and use DDA-08 and DDA-16 boards.
The manual is intended for data acquisition system designers, engineers,
technicians, scientists, and other users responsible for setting up, cabling,
and wiring signals to DDA-08 and DDA-16 boards. It is assumed that
users are familiar with data acquisition principles and with their particular
application.
The DDA-08/16 User’s Guide is organized as follows:
●
Section 1 provides an overview of the features of DDA-08 and
DDA-16 boards, including a description of supporting software and
accessories.
●
Section 2 provides a detailed description of the features of DDA-08
and DDA-16 boards.
●
Section 3 describes how to unpack, configure, and install DDA-08
and DDA-16 boards.
Section 4 describes how to attach accessory boards and how to wire
●
signals to DDA-08 and DDA-16 boards.
Section 5 describes how to use the Control Panel to test the functions
●
of DDA-08 and DDA-16 boards under Windows
Section 6 describes how to calibrate and test the functions of DD A-08
●
.
and DDA-16 boards under DOS.
Section 7 provides troubleshooting information.
Appendix A lists the specifications for DDA-08 and DDA-16 boards.
●
Appendix B lists the connector pin assignments.
●
An index completes this manual.
Throughout the manual, references to DDA-08/16 boards apply to both
DDA-08 and DDA-16 boards. When a feature applies to a particular
board, that board’s name is used.
An onboard internal pacer clock is provided; you select the update
rate through software.
An external pacer clock is supported.
1-1
An onboard output clock is provided; you can use the output clock to
●
synchronize other devices to the pacer clock.
●
An external digital trigger is supported.
●
An external gate is supported.
●
An interrupt can be generated when analog output channels are
updated.
Supporting Software
The following software is available for operating DDA-08/16 boards:
●
DDA-08/16 standard software package — Shipped with
DDA-08/16 boards. Includes DriverLINX for Microsoft Windows
and function libraries for writing application programs under
Windows in a high-level language such as Microsoft Visual Basic,
Microsoft Visual C++, Delphi, utility programs, and
language-specific example programs.
DriverLINX — The high-performance real-time data-acquisition
●
device drivers for Windows application development including:
●
DriverLINX API DLLs and drivers supporting the DDA-08/16
hardware.
Analog I/O Panel — a DriverLINX program that verifies the
●
installation and configuration of DriverLINX to your DD A-08/16
board and demonstrates several virtual bench-top instruments.
Learn DriverLINX — an interactive learning and demonstration
●
program for DriverLINX that includes a Digital Storage
Oscilloscope.
Source Code — for the sample programs.
●
●
DriverLINX Application Programming Interface Files — for the
DDA-08/16 compiler.
●
DriverLINX On-line Help System — provides immediate help as
you operate DriverLINX.
●
Supplemental Documentation — on DriverLINX installation and
configuration; analog and digital I/O programming; counter/timer
programming; technical reference; and information specific to the
DDA-08/16 hardware.
that allow you to access the functions of the board; provides a
breadboard area with power and additional screw terminals to access
the user-designed circuitry.
●
STP-37 screw terminal panel — Provides 37 screw terminals that
allow you to access the functions of the board; av ailable with a plastic
case (STP-37/C) that you can mount in a standard DIN rail.
●
C-1800 cable — Unshielded, 18-inch cable with a 37-pin connector
on each end; allows you to connect a DDA-08/16 board to an STA-U
or STP-37. (Note that the C-1800 cable is also available in longer
lengths, if required.)
●
Refer to Keithley’s Products catalog or contact your local sales office for
information on obtaining these accessories.
S-1800 cable — Shielded, 18-inch cable with a 37-pin connector on
each end; allows you to connect a DDA-08/16 board to an STA-U or
STP-37. (Note that the S-1800 cable is also available in longer
lengths, if required.)
1-3
2
Functional Description
This section describes the analog output features of DDA-08/16 boards. A
functional block diagram of a DDA-08/16 board is shown in Figure 2-1.
Note that quad DAC2 and quad DAC3 are available on DDA-16 boards
only.
DDA-08 boards contain two quad DACs (quad DAC0 and quad DAC1),
which provide eight analog output channels. DDA-16 boards contain four
quad DACs (quad DAC0, quad DAC1, quad DAC2, and quad DAC3),
which provide 16 analog output channels. Quad DAC0 contains channels
0 through 3; quad DAC1 contains channels 4 through 7; quad DAC2
contains channels 8 through 11; quad DA C3 contains channels 12 through
15.
Each analog output channel contains an input buffer for storing data.
Through software, the host computer loads a single value into the input
buffer of a single channel or loads multiple v alues into the input buf fers of
a sequence of consecutive channels. The analog output values are held in
the input buffers until the channels are updated. At that point, the values
currently held in the input buffers are written to the channels, updating
their output values.
You can update a single analog output channel immediately when the
input buffer is loaded, or you can update several analog output channels
simultaneously using a pacer clock. Refer to page 2-6 for more
information about pacer clocks.
If you want to update several analog output channels simultaneously, you
use software to include one or more quad DACs in the update group. All
channels on the quad DACs in the update group are updated
simultaneously at each pulse of the pacer clock.
Note:
In multi-channel mode, the DDA-08/16 writes all data to a
consecutive range of analog channels.
●
If the Start Channel is greater than the Stop Channel, the channel
sequence is [Start Channel, ..., Last Channel, 0, ..., Stop Channel],
where Last Channel is the highest numbered channel for the
DDA-08/16 model the application is using.
●
The DDA-08/16 can optionally output to all DACs in the range
simultaneously, or write to one DAC in the range at each timing
event.
In multi-channel list mode, the DDA-08/16 writes all data to a random list
of analog channels.
●
The channel-gain list may contain channels in any order but only with
unity gain. In simultaneous mode, the list may not repeat the same
channel.
●
The DDA-08/16 can optionally output to all DACs in the list
simultaneously, or write to one DAC in the list at each timing event.
Refer to the Using DriverLINX with Your Hardware, Keithle y DDA-08/16
manual that accompanies your DriverLINX software.
DDA-08/16 boards support both voltage output and current output. You
select the output signal for each quad DAC using the output signal
switches on the board. Refer to page 3-14 for more information.
Voltage output and current output ranges are described as follows:
●
Voltage output — For voltage output, you can select one of five
ranges (0 to 10V, 0 to 5V, ±10V, ±5V, or ±2.5V) for each quad DAC.
You select the voltage output range using two switches on the board.
The output span switch determines the span (5V, 10V, or 20V); the
output range type switch determines the output range type (unipolar
or bipolar). Refer to page 3-15 and page 3-17 for more information.
Table 2-1 shows the voltage output ranges provided by each span and
output range type.
Do not select a 20V span with a unipolar output range
type. If you do, the output will saturate at about 10V with
approximately a half scale input to the quad DAC.
Notes:
All channels on a quad DAC have the same voltage output
range; you cannot select a voltage output range on a
channel-by-channel basis.
Make sure that you select a voltage output range that includes all the
output values required by the device connected to your board. In
addition, make sure that the range does not exceed the required values
excessively; this ensures the best possible resolution and prevents
potential damage to the device.
Current output — For current output, the range is always 4 to 20
●
mA. For current output, you must set the output range type and the
output span switches on the board to current output. Refer to page
3-15 and page 3-17 for more information.
Each analog output channel has a resolution of 12 bits, which translates to
a raw count value between 0 and 4095. For bipolar voltage output ranges,
a value of 0 represents negative full scale and a value of 4095 represents
positive full scale. For unipolar voltage output ranges, a value of 0
represents 0V and a value of 4095 represents positive full scale. For
current output ranges, a value of 0 represents 4mA and a value of 4095
represents 20mA.
Note:
To ensure that the analog output channels power-up to a known
state, the output value from all channels configured for voltage output is
nominally 0V at power-up and the output value from all channels
configured for current output is nominally 0mA at power-up.
DDA-08/16 boards support two types of clocks: a pacer clock and an
output clock. These clocks are described in the following sections.
The pacer clock determines the update rate (the time between each update
of all the channels on the quad DACs in the update group). DDA-08/16
boards provide the following software-selectable pacer clocks:
Hardware internal pacer clock — The internal pacer clock uses an
●
onboard time base. The internal pacer clock determines the update
rate by multiplying a prescaler value (1
µ
s, 10
µ
s, 100
µ
s, 1ms, 10ms,
100ms, or 1s) by an 8-bit counter value. The prescaler values provide
a wide range of update rates; the 8-bit counter value provides the
resolution that allows you to achieve the exact update rate you
require.
The time between updates can range from 1
s to 4.267 minutes.
µ
For example, assume that you want to update the channels every
50ms. The prescaler value can be 1ms and the counter value can
be 50, or the prescaler value can be 10ms and the counter value can
be 5.
Notes:
The prescaler value used by the pacer clock is also used to
determine the length of the output clock pulse and the time delay between
the update of the analog output channels on the quad DACs in the update
group and the output clock pulse. Refer to page 2-8 for more information
about the output clock.
DriverLINX allo ws you to specify the Logical Channel (0 = Pacer Clock,
1 = Output Clock), Clock Source, Clock Tic Period, Mode, and Gate.
Refer to the Using DriverLINX with Your Hardware, Keithle y DDA-08/16
manual that accompanies your DriverLINX software.
When the pacer clock counter is loaded, the channels on the quad
DACs in the update group are updated and the pacer clock counter
starts counting down. (Note that a slight time delay occurs between
the time the pacer clock counter is loaded and the time the channels
are updated.) When the pacer clock counter counts down to zero, all
the channels on the quad DA Cs in the update group are updated again
and the process repeats.
●
Hardware external pacer clock — An e xternal pacer clock is useful
if you want to update the channels at rates not available with the
internal clock, if you want to update the channels at uneven intervals,
or if you want to update the channels based on an external event.
The external pacer clock is an externally applied TTL-compatible
signal, which you attach to the CLOCK IN pin (pin 1) of the main I/O
connector. At each active edge of the external pacer clock, the
channels are updated. The active edge is software-selectable; at
power-up, the board assumes that the acti ve edge for an external pacer
clock is a falling edge.
Figure 2-2 illustrates how analog output channels are updated when using
an internal pacer clock and when using an external pacer clock with a
falling edge as the active edge. (Note that Figure 2-2 assumes that you are
not using a hardware trigger; refer to Figure 2-4 on page 2-12 when using
a hardware trigger.)
When determining the update rate for a hardware pacer clock
(internal or external), make sure that you do not update the analog output
channels faster than the host computer writes to the input buffers of the
channels. Typical update rates range from 1kHz to 20kHz; the actual rate
depends on a number of factors, including your computer, the operating
system/environment, and software issues. Also keep in mind the settling
time of the channels on the DDA-08/16 board; refer to Appendix A for
information.
At power-up, the pacer clock is disabled.
If enabled, the output clock generates an output pulse for each update of
the analog output channels on the quad DACs in the update group (using
either the internal pacer clock or the external pacer clock). You can use
this output pulse to synchronize other devices to the pacer clock.
The output pulse is issued from the CLOCK OUT pin (pin 20) of the
main I/O connector. The polarity of the output pulse (falling edge or
rising edge) is software-selectable. If you select a falling-edge pulse, the
output from CLOCK OUT starts high; if you select a rising-edge pulse,
the output from CLOCK OUT starts low. On power-up, the board
assumes that you want to generate a falling-edge pulse.
Time Delay
Through software, you can specify a time delay between the update of the
analog output channels on the quad DACs in the update group and the
output clock pulse. The output clock determines the time delay by
multiplying the prescaler value used by the internal pacer clock by the
output clock’s own independent 8-bit counter value. The output clock
counter is reloaded each time the analog output channels are updated.
For example, if the prescaler value is 1ms and you want a 30ms time
delay between the update of the analog output channels and the output
clock pulse, the output clock counter value must be 30.
If the output clock counter value is 0, the output clock pulse is
generated simultaneously with the update of the analog output channels
(no delay).
The DDA-08/16 can write analog output samples after the hardware
detects a digital trigger condition. Use post-triggering in DriverLINX
when you want to synchronize the start of data acquisition with an
external signal. Digital Start Events contain mask, pattern, and match
fields. The mask is logically ANDed with the digital input data on the
Logical Channel and then compared with the pattern for a
match/mismatch.
●
Specify the Channel as 0 .
●
Specify the Mask and Pattern properties as 1 to specify the bit
position of the 1-bit trigger input.
●
Specify the Match property as Not equals to trigger on the edge of
the trigger input.
●
Specify the Delay property as any number of samples from
32
0 to 2
Connect the signal to the TRIGGER IN line.
●
- 1.
Refer to Using DriverLINX with Your Hardware, Keithley DDA-08/16
manual that accompanies your DriverLINX software.
The period of the output pulse is equal to the prescaler value. Since the
prescaler generates a square wave, the length of the output pulse is equal
to half of the prescaler value. For example, if the prescaler v alue is 10 ms,
the length of the output pulse is 5ms.
Figure 2-3 illustrates a falling-edge output pulse that is 5ms in length
(prescaler value is 10ms) and is generated 30ms after the analog output
channels on the quad DACs in the update group are updated. Since there
is only one prescaler, the prescaler v alue must be 10ms for both the pacer
clock and the output clock.
In DriverLINX, Timing Events specify how the hardware paces or clocks
the sample output. DriverLINX uses the Timing Event to program when
the DDA-08/16 writes the next analog output sample to the DACs.
The DDA-08/16 supports the following Timing Events:
None — Output requires no pacing as DriverLINX is writing only a
●
single value.
Rate — The DDA-08/16 supports only fixed rate analog output using
●
internal and external clocks. The Rate Generator provides a fix ed rate
clock with equal time intervals between tics. An internally clocked
Rate Generator produces a fixed rate clock with equal time intervals
between tics. An externally clocked Rate Generator produces a rate
clock with unknown time intervals between tics.
●
Hardware Trigger
You can enable a hardware trigger through software. A hardware trigger is
an externally applied, edge-sensitive, digital signal that determines when
the analog output channels on the quad DACs in the update group can
respond to either an internal or an external pacer clock.
You connect the digital trigger signal to the TRIGGER IN pin (pin 2) of
the main I/O connector. If the trigger is enabled, the board waits for an
active edge on TRIGGER IN. The active edge is software-selectable; at
power-up, the board assumes that the acti v e edge for a hardware trigger is
a falling edge.
When the board detects an active edge, the channels respond to each pulse
of the pacer clock until the trigger circuitry is disabled.
The actual point at which the channels are updated depends on whether
you are using an internal pacer clock or an external pacer clock. These
considerations are described as follows:
Digital — DriverLINX uses an external digital input signal to pace
Internal pacer clock — The internal pacer clock remains idle until
the trigger event occurs. When the trigger event occurs, the pacer
clock counter is loaded and the channels are updated. (Note that a
slight time delay occurs between the time the pacer clock counter is
loaded and the time the channels are updated.)
2-11
Hardware Trigger
(Rising Edge)
External pacer clock — When the trigger event occurs, the board
●
begins monitoring the state of the external pacer clock signal. At the
next active edge of the external pacer clock, the channels are updated.
Figure 2-4 illustrates how the channels are updated when using a
rising-edge hardware trigger.
Trigger event occurs
External Pacer Clock
(Falling Edge)
Internal Clock
Source
Note:
depends on the pacer clock. Refer to page 2-6 for more information.
Updates begin when
using an external
pacer clock
(idle state)
count
Updates begin when
using an internal
pacer clock
count
count
count
Figure 2-4. Using a Hardware Trigger
The time at which the analog output channels are updated also