National Instruments NI MID-7604 User manual

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USER GUIDE
MID-7604/7602 Power Drive
This user guide describes the electrical and mechanical aspects of the
MID-7604/7602 power drive and how to use the power drive with your
motion controller.
Contents
Conventions ............................................................................................ 2
Introduction............................................................................................. 3
What You Need to Get Started ............................................................... 3
Compliance with FCC/Canada Radio Frequency Interference
Regulations........................................................................................... 4
Safety Information .................................................................................. 5
Front Panel Switches............................................................................... 8
Back Panel Connector Wiring................................................................. 9
Host Bus Interlock Circuit ...................................................................... 10
Front Panel LEDs.................................................................................... 10
Driver Fault Output LEDs ............................................................... 11
Driver Inhibit LEDs ......................................................................... 11
Limit Status LEDs ........................................................................... 11
Front Panel DIP Switch Settings............................................................. 12
Microstepping Selection .................................................................. 12
Output Current Settings ................................................................... 13
Inhibit Input Polarity Setting ........................................................... 15
Limit Status LED Polarity Setting ................................................... 16
Back Panel Connector Wiring................................................................. 16
Motor Power Terminal Blocks ........................................................ 16
Encoder Terminal Blocks ................................................................ 17
Limit Switch Terminal Blocks......................................................... 20
Breakpoint and Trigger Terminal Blocks ........................................ 20
Analog I/O Terminal Blocks............................................................ 21
Accessories for Optional Use.................................................................. 22
Amplifier/Driver Command Signals....................................................... 23
Stepper Motor Configurations ................................................................ 24
Specifications .......................................................................................... 26
Where to Go for Support......................................................................... 31

MID-7604/7602 Power Drive User Guide 2 ni.com
Conventions
The following conventions are used in this manual:
»The »symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash. When this symbol is marked on a
product, refer to the Specifications section of this guide for information
about precautions to take.
This icon denotes a warning, which advises you of precautions to take to
avoid being electrically shocked. When symbol is marked on a product, it
denotes a warning advising you to take precautions to avoid electrical
shock.
When symbol is marked on a product, it denotes a component that may be
hot. Touching this component may result in bodily injury.
bold Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.

©National Instruments Corporation 3 MID-7604/7602 Power Drive User Guide
Introduction
The National Instruments MID-7604/7602 power drive is a complete
power amplifier and system interface for use with four or two axes of
simultaneous stepper motion control. Ideally suited to industrial and
laboratory applications, the MID-7604/7602 has everything you need to
connect motors, encoders, limit switches, I/O, and other motion hardware
to National Instruments motion controllers.
The MID-7604/7602 can drive a broad range of stepper motors with its
rugged microstepping bipolar chopper driver and user-selectable
current-per-phase settings. In all configurations, power supplies are built-in
and use standard 230/115 VAC for operation. Electronics are fan-cooled to
assure reliable operation.
The MID-7604/7602 simplifies field wiring through separate encoder, limit
switch, and motor power removable screw terminal connector blocks for
each axis. The terminal blocks do not require special wiring tools for
installation. The MID-7604/7602 connects to National Instruments motion
controllers using a 68-pin, high-density interconnect cable.
The MID-7604/7602 has four levels of amplifier inhibit/disable protection
for motion system shutdown. The front panel contains both enable and
power switches for direct motor inhibiting and system power-down
operations. The MID-7604/7602 also has a host bus power interlock that
activates an internal driver inhibit signal if the host computer is shut down
or the motion controller interface cable is disconnected. The inhibit input
from the back panel connectors also inhibits the stepper drives when
activated.
The MID-7604/7602 is packaged in a rugged, lightweight enclosure that
can be used as a benchtop unit, panel mounted using a panel-mount kit,
or rack mounted using a 19-inch standard rack kit.
What You Need to Get Started
To set up and use your MID-7604/7602 accessory, you must have the
following items:
❑MID-7604/7602 power drive
❑Power cord (IEC type)
❑Panel-mount kit (part number 187243-01)

MID-7604/7602 Power Drive User Guide 4 ni.com
❑One of the following shielded cable assemblies, as applicable:
– SH68-C68-S (part number 186381-02)
– SHC68-C68-S (part number 186380-02)
For detailed specifications for the MID-7604/7602 power drive, refer to the
Specifications section of this guide.
Compliance with FCC/Canada Radio Frequency
Interference Regulations
Determining FCC Class
The Federal Communications Commission (FCC) has rules to protect
wireless communications from interference. The FCC places digital
electronics into two classes. These classes are known as Class A (for use in
industrial-commercial locations only) or Class B (for use in residential
or commercial locations). All National Instruments (NI) products are
FCC Class A products.
Depending on where it is operated, this Class A product could be subject
to restrictions in the FCC rules. (In Canada, the Department of
Communications (DOC), of Industry Canada, regulates wireless
interference in much the same way.) Digital electronics emit weak signals
during normal operation that can affect radio, television, or other wireless
products.
All Class A products display a simple warning statement of one paragraph
in length regarding interference and undesired operation. The FCC rules
have restrictions regarding the locations where FCC Class A products can
be operated.
Consult the FCC Web site at www.fcc.gov for more information.
FCC/DOC Warnings
This equipment generates and uses radio frequency energy and, if not
installed and used in strict accordance with the instructions in this manual
and the CE marking Declaration of Conformity1, may cause interference to
radio and television reception. Classification requirements are the same for
the Federal Communications Commission (FCC) and the Canadian
Department of Communications (DOC).
1 The CE marking Declaration of Conformity contains important supplementary information and instructions for the user or
installer.

©National Instruments Corporation 5 MID-7604/7602 Power Drive User Guide
Changes or modifications not expressly approved by NI could void the
user’s authority to operate the equipment under the FCC Rules.
Class A
Federal Communications Commission
This equipment has been tested and found to comply with the limits for a
Class A digital device, pursuant to part 15 of the FCC Rules. These limits
are designed to provide reasonable protection against harmful interference
when the equipment is operated in a commercial environment. This
equipment generates, uses, and can radiate radio frequency energy and,
if not installed and used in accordance with the instruction manual, may
cause harmful interference to radio communications. Operation of this
equipment in a residential area is likely to cause harmful interference in
which case the user is required to correct the interference at their own
expense.
Canadian Department of Communications
This Class A digital apparatus meets all requirements of the Canadian
Interference-Causing Equipment Regulations.
Cet appareil numérique de la classe A respecte toutes les exigences du
Règlement sur le matériel brouilleur du Canada.
Compliance with EU Directives
Users in the European Union (EU) should refer to the Declaration of
Conformity (DoC) for information1pertaining to the CE marking. Refer to
the Declaration of Conformity (DoC) for this product for any additional
regulatory compliance information. To obtain the DoC for this product,
visit ni.com/certification, search by model number or product line,
and click the appropriate link in the Certification column.
Safety Information
Caution The following paragraphs contain important safety information you must follow
when installing and operating the device.
Do not operate the device in a manner not specified in the documentation.
Misuse of the device may result in a hazard and may compromise the safety
protection built into the device. If the device is damaged, turn it off and do
1 The CE marking Declaration of Conformity contains important supplementary information and instructions for the user or
installer.

MID-7604/7602 Power Drive User Guide 6 ni.com
not use it until service-trained personnel can check its safety. If necessary,
return the device to National Instruments for repair.
Keep away from live circuits. Do not remove equipment covers or shields
unless you are trained to do so. If signal wires are connected to the device,
hazardous voltages can exist even when the equipment is turned off. To
avoid a shock hazard, do not perform procedures involving cover or shield
removal unless you are qualified to do so. Disconnect all field power prior
to removing covers or shields.
If the device is rated for use with hazardous voltages (>30 Vrms, 42.4 Vpk,
or 60 Vdc), it may require a safety earth-ground connection wire. Refer to
the device specifications for maximum voltage ratings.
Because of the danger of introducing additional hazards, do not install
unauthorized parts or modify the device. Use the device only with the
chassis, modules, accessories, and cables specified in the installation
instructions. All covers and filler panels must be installed while operating
the device.
Do not operate the device in an explosive atmosphere or where flammable
gases or fumes may be present. Operate the device only at or below the
pollution degree stated in the specifications. Pollution consists of any
foreign matter—solid, liquid, or gas—that may reduce dielectric strength
or surface resistivity. The following is a description of pollution degrees.
• Pollution Degree 1 means no pollution or only dry, nonconductive
pollution occurs. The pollution has no effect.
• Pollution Degree 2 means that only nonconductive pollution occurs in
most cases. Occasionally, however, a temporary conductivity caused
by condensation must be expected.
• Pollution Degree 3 means that conductive pollution, or dry,
nonconductive pollution occurs that becomes conductive due to
condensation.
Clean the device and accessories by brushing off light dust with a soft,
nonmetallic brush. Remove other contaminants with a stiff, nonmetallic
brush. The unit must be completely dry and free from contaminants before
returning it to service.
You must insulate signal connections for the maximum voltage for which
the device is rated. Do not exceed the maximum ratings for the device.
Remove power from signal lines before connection to or disconnection
from the device.

©National Instruments Corporation 7 MID-7604/7602 Power Drive User Guide
The MID 7604/7602 drive is not a measurement device. However, if you
want to make a measurement of the circuits or devices connected to the
drive, operate the device only at or below the installation category stated in
the specifications. Installation categories are listed below.
Measurement Category1: Measurement circuits are subjected to working
voltages2and transient stresses (overvoltage) from the circuit to which they
are connected during measurement or test. Measurement Category
establishes standardized impulse withstand voltage levels that commonly
occur in electrical distribution systems. The following is a description of
measurement categories:
• Measurement Category I is for measurements performed on circuits
not directly connected to the electrical distribution system referred to
as MAINS3voltage. This category is for measurements of voltages
from specially protected secondary circuits. Such voltage
measurements include signal levels, special equipment, limited-energy
parts of equipment, circuits powered by regulated low-voltage sources,
and electronics.
• Measurement Category II is for measurements performed on circuits
directly connected to the electrical distribution system. This category
refers to local-level electrical distribution, such as that provided by
a standard wall outlet (for example, 115 V for U.S. or 230 V for
Europe). Examples of Installation Category II are measurements
performed on household appliances, portable tools, and similar
devices/modules.
• Measurement Category III is for measurements performed in the
building installation at the distribution level. This category refers to
measurements on hard-wired equipment such as equipment in fixed
installations, distribution boards, and circuit breakers. Other examples
are wiring, including cables, bus-bars, junction boxes, switches,
socket-outlets in the fixed installation, and stationary motors with
permanent connections to fixed installations.
• Measurement Category IV is for measurements performed at the
primary electrical supply installation (<1,000 V). Examples include
electricity meters and measurements on primary overcurrent
protection devices and on ripple control units.
1 Measurement categories, also referred to as installation categories, are defined in electrical safety standard IEC 61010-1.
2 Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.
3 MAINS is defined as the (hazardous live) electrical supply system to which equipment is designed to be connected for the
purpose of powering the equipment. Suitably rated measuring circuits may be connected to the MAINS for measuring
purposes.

MID-7604/7602 Power Drive User Guide 8 ni.com
Warning The stepper motor connectors on this drive are energized when the unit is
powered on. Disconnect the MID-7604/7602 unit from the power outlet before connecting
wires to or disconnecting wires from the stepper connectors. Strip back the insulation of
the stepper wires to the stepper connectors no more than 7 mm. Failure to do so could
result in electric shock leading to serious bodily injury or death.
Hot Surface The bottom surface of the MID-7604/7602 can get very hot to the touch under
certain conditions. To avoid a burn hazard, refer to Output Current Settings in the Front
Panel DIP Switch Settings section of this guide for the appropriate current setting and
safety hazards.
Front Panel Switches
Figure 1 shows the front panel of your MID-7604/7602. The DIP switches
are shown with the detachable metal cover plate removed.
Figure 1. MID-7604/7602 Front Panel
Note Items followed by an asterisk (*) are available on the MID-7604 only.
The two rocker switches on the MID-7604/7602 front panel are the
AC POWER and ENABLE. Figure 1 shows the location of these switches.
The AC POWER switch energizes the motor bus (+24 V) and the logic
(+5 V) power supplies. When switched on, the green power LED labeled
+5 V illuminates. If this LED fails to illuminate, check the power cord and
main input fuse on the front panel.
The ENABLE switch enables or inhibits the stepper drivers. If the
ENABLE switch is in the inhibit position (off), the stepper drivers are
inhibited, and the yellow LEDs (the middle row of the LED status array)
and red LEDs (the top row of the LED status array) illuminate for all axes.
Refer to the Front Panel LEDs section of this guide for more information.
1 Main Input Fuse
2 Line Voltage Select Switch
3PowerSwitch
4 Green Power LED
5 Enable Switch
6 Axis 1 DIP Switch Bank
7 Axis 2 DIP Switch Bank
8 Axis 3 DIP Switch Bank*
9 Axis 4 DIP Switch Bank*
10 LED Status Array
FUSE
LINE VOLTAGE SELECT
AC POWER
1
AXIS
234
ON OFF +5V
ON OFF
ENABLE
AXIS CONFIGURATION
1 2 3 4 105 6 7 8 9
ON ON ON ON
FAULTS
INHIBITS
LIMITS

©National Instruments Corporation 9 MID-7604/7602 Power Drive User Guide
Note In older versions of the MID-7604/7602, the red status LEDs do not illuminate when
the yellow status LEDs illuminate. This behavior only occurs in newer versions of the
MID-7604/7602.
Both the AC POWER and ENABLE switches can inhibit the stepper
drivers. However, as long as the AC POWER switch is on, only the stepper
driver output stages are disabled. The remaining circuitry remains active,
including the quadrature encoder circuit.
Caution You must change the MID-7604/7602 main input fuse on the front panel if you
change the line voltage from the factory setting. Refer to the Specifications section of this
guide for fuse specifications.
Back Panel Connector Wiring
Figure 2 shows the connectors located on the back panel of your
MID-7604/7602.
Figure 2. MID-7604/7602 Back Panel Connectors
Note Items followed by an asterisk (*) are available on the MID-7604 only.
Caution Be sure to turn off the ENABLE switch and the main AC power to your
MID-7604/7602 and host computer before connecting the accessory to your motion
controller.
Warning The stepper motor connectors on this drive are energized when the unit is
powered on. Disconnect the MID-7604/7602 unit from the power outlet before connecting
wires to or disconnecting wires from the stepper connectors. Strip back the insulation of
the stepper wires to the stepper connectors no more than 7 mm. Failure to do so could
result in electric shock leading to serious bodily injury or death.
1 Motion Controller Connector
2 Analog Input Connector
3 Analog Output Connector
4 Trigger Connector
5 Breakpoint Connector
6 AC Power
Encoder
Connectors
7Axis1
8Axis2
9Axis3*
10 Axis 4*
Limit
Connectors
11 Axis 1
12 Axis 2
13 Axis 3*
14 Axis 4*
Motor
Connectors
15 Axis 1
16 Axis 2
17 Axis 3*
18 Axis 4*
1 2 3 4 5
78
11 12
910
13 14
15 16 17 18
6

MID-7604/7602 Power Drive User Guide 10 ni.com
1. Use the interface cable to connect the motion controller to the
MID-7604/7602. Wire the motor power, limit switch, encoder, and I/O
terminal blocks as described in this guide and to your specific system
requirements.
Caution You must change the MID-7604/7602 main input fuse on the front panel if you
change the line voltage from the factory setting. Refer to the Specifications section of this
guide for fuse specifications.
2. Use the LINE VOLTAGE SELECT switch to configure the
MID-7604/7602 for 115 VAC, 60 Hz or 230 VAC, 50 Hz operation.
For proper operation, you must set this switch to match your power
source.
3. Finally, install the power cord into the back panel AC connector and
plug it in to a correctly rated power source.
Host Bus Interlock Circuit
The MID-7604/7602 has a host bus interlock circuit that monitors the
presence of +5 V from the host computer and disables the MID-7604/7602
when the voltage is not present or falls out of tolerance. This circuit shuts
down the stepper drives for all axes by activating the inhibit when the host
computer is disconnected from the MID-7604/7602 or inadvertently shut
down. Activation of the host bus interlock circuitry illuminates the yellow
LEDs (middle row) and red LEDs (top row) of the LED status array for all
axes. Refer to the Front Panel LEDs section ofthisguide for more
information.
Note In older versions of the MID-7604/7602, the red status LEDs do not illuminate when
the yellow status LEDs illuminate. This behavior only occurs in newer versions of the
MID-7604/7602.
Front Panel LEDs
The front panel LEDs consist of a single green LED to indicate if the main
power is active and an LED status array of 3 rows by 4 columns that
provides a variety of status information. Refer to Figure 1 for the location
of the front panel LEDs.
If the DC power supplies are active, the green power LED illuminates.
If this LED fails to illuminate, check the power cord and the main input
fuse on the front panel.
The LED status array is arranged by motor axes. Each of the four columns
represents an axis, and each of the three rows represents a particular status.

©National Instruments Corporation 11 MID-7604/7602 Power Drive User Guide
Table 1 summarizes the axis and corresponding status for each LED in the
3×4array.
Driver Fault Output LEDs
The top row of LEDs indicates the status of the stepper drivers. An LED
illuminates red when an overcurrent condition or a problem with the motor
bus voltage on that axis occurs. The LEDs also illuminate red when the axis
is inhibited. Referto the Driver Inhibit LEDs section of thisguide for more
information about inhibit conditions.
Note In older versions of the MID-7604/7602, the red status LEDs do not illuminate when
the yellow status LEDs illuminate. This behavior only occurs in newer versions of the
MID-7604/7602.
Driver Inhibit LEDs
The middle row of LEDs indicates whether or not a motor axis is inhibited.
An axis is inhibited and the LED illuminates yellow in the following
instances:
• if the host bus interlock circuitry is activated
•iftheENABLE switch on the front panel is in the inhibit (off) position
• if the motion controller’s inhibit signal is low
• if the per-axis inhibit input is actively driven
The polarity of the per-axis inhibit input is selectable from the front panel
DIP switches. Refer to the Front Panel DIP Switch Settings section of this
guide for more information.
Limit Status LEDs
The bottom row of LEDs indicates whether or not a limit switch is currently
active. The LED illuminates green if either the forward or reverse limit
switch is active for each axis. You can select the polarity for the limit status
LEDs from the front panel DIP switches. Refer to the Front Panel DIP
Switch Settings section of this guide for more information.
Table 1. Front Panel LED Indicators
Status Motor Axis
Driver Fault Output (red) 1 2 3 4
Driver Inhibit (yellow) 1 2 3 4
Limit Status (green) 1 2 3 4

MID-7604/7602 Power Drive User Guide 12 ni.com
Front Panel DIP Switch Settings
The MID-7604/7602 front panel has a detachable metal plate that when
removed provides access to four 10-position DIP switch banks. Refer to
Figure 1 for the location of these switches.
Use the first nine DIP switches on each 10-position DIP switch bank to
configure the microstep rate, peak output current, and current reduction for
each axis. The DIP switch banks for axes 1 and 2 contain a global DIP
switch, switch 10, which sets the polarity of the inhibit input and the
polarity of the limit status LED, respectively. Figure 3 shows the DIP
switch bank layout.
Figure 3. DIP Switch Bank Layout
Microstepping Selection
The MID-7604/7602 uses bipolar chopper, two-phase microstepping
drivers with a broad range of microstep rates. The factory default setting
is 10-times microstepping (2,000 steps/rev with standard 1.8º stepper
motors). Table 2 shows the DIP switch settings for all possible microstep
settings. DIP switches 6 through 9 control the microstep rate on a per-axis
basis.
1 Peak Current Output Switches
2 Microstep Rate Switches
3 Current Reduction Switch
4 Global Polarity Switch (unused on
axes 3 and 4 DIP switch banks)
12345678910
O
N
1 2
3 4

©National Instruments Corporation 13 MID-7604/7602 Power Drive User Guide
Output Current Settings
The MID-7604/7602 can provide 0.20 to 1.4 A peak (0.14 to 1 A RMS),
depending on the peak output current DIP switch settings for each axis.
DIP switches 1 through 4 control the peak output current. Table 3 shows
the DIP switch settings for all possible peak output current settings.
Table 2. Microstep Rate DIP Switch Setting
Binary Selections Decimal Selections
Switch Microsteps/Step Switch Microsteps/Step
2 (half step) 5
4 10
(factory default)
8 25
16 50
32 125
64 250
128 Do not use
256 Do not use
Table 3. Peak Output Current DIP Switch Setting
Switch Peak Output (A) Switch Peak Output (A)
1.40 0.35
1.20 0.30
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
6
O
N
78 9 6
O
N
78 9
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4

MID-7604/7602 Power Drive User Guide 14 ni.com
If you are connecting multiple motors to your MID-7604/7602, verify that
the total power dissipated by the motors at any given time is less than the
total power the drive can provide. If the total power requirement exceeds
the capability of the drive at any point, the drive will provide less power to
the motors than desired until the total power requirement drops back down.
The MID-7604/7602 may overheat under continuous operation with loads
that exceed specified limits.
Caution A fire safety hazard exists when the total power dissipated by the motors exceeds
80 W continuous for a sustained period of time.
To determine the maximum total power dissipation of all of the motors
combined, add up the maximum power each motor can dissipate. If this
value is less than or equal to 80 W continuous, you will not exceed the
capabilities of the MID-7604/7602.
If the value is greater than 80 W continuous, you may still be within the
operating capabilities of the MID-7604/7602, since it is unlikely you will
run all of your motors simultaneously at their maximum levels. Make a
reasonable estimation of the maximum power your motors will require at
any given time and verify that this value is less than 80 W continuous.
You can configure the MID-7604/7602 stepper drivers in a current
reduction mode on a per-axis basis. This configuration is useful to
minimize motor heating when you are not stepping. With current reduction
1.00 0.28
0.85 0.27
0.70 0.25
0.60 0.24
0.55 0.23
0.50
(factory default)
0.20
Table 3. Peak Output Current DIP Switch Setting (Continued)
Switch Peak Output (A) Switch Peak Output (A)
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4
1
O
N
23 4 1
O
N
23 4

©National Instruments Corporation 15 MID-7604/7602 Power Drive User Guide
enabled, the current decreases by 50% when no stepping has occurred for
approximately 500 ms. DIP switch 5 controls current reduction on a
per-axis basis. When this DIP switch is on, current reduction is enabled.
When this DIP switch is off, current reduction is disabled. The factory
default setting is current reduction enabled.
Table 4 shows the available settings for DIP switch 5.
Inhibit Input Polarity Setting
The MID-7604/7602 has a DIP switch that globally sets the polarity for the
inhibit input for all axes. DIP switch 10 on the axis 1 DIP switch bank
controls this setting. Refer to Figures 1 and 3 for the location of this switch.
The factory default setting of DIP switch 10 is active low. If the inhibit
input is active, the axis is inhibited and the yellow status LED (middle row)
and red status LED (top row) illuminates for the axis.
Note In older versions of the MID-7604/7602, the red status LEDs do not illuminate when
the yellow status LEDs illuminate. This behavior only occurs in newer versions of the
MID-7604/7602.
Table 5 shows the DIP switch setting for the inhibit input polarity selection.
Table 4. Current Reduction DIP Switch Settings
Switch Setting Operation
Current reduction enabled
(factory default)
Current reduction disabled
Table 5. Inhibit Input Polarity DIP Switch Settings
Axis 1 Switch Setting Operation
Active high
Active low
(factory default)
5
O
N
5
O
N
10
O
N
10
O
N

MID-7604/7602 Power Drive User Guide 16 ni.com
Limit Status LED Polarity Setting
The MID-7604/7602 has a DIP switch that globally sets the polarity for the
Limit Status LED. DIP switch 10 on the axis 2 DIP switch bank controls
this setting. Refer to Figures 1 and 3 for the location of this switch.
The factory default setting is active low. Typically, you set the switch to
match your controller’s polarity setting, so that if either the reverse or
forward limits for an axis are active, the green status LED (on the bottom
row) for the axis illuminates. This DIP switch alters only the polarity for
the LEDs, and not the actual limit to the motion controller. Table 6 shows
the DIP switch setting for the Limit Status LED polarity selection.
Back Panel Connector Wiring
Motor Power Terminal Blocks
Each axis on the MID-7604/7602 has a separate 5-position removable
screw terminal block for motor power wiring. Figure 4 shows a typical
stepper motor configuration pin assignment.
Note The dotted loop indicates a shielded cable. A line above a signal indicates that the
signal is active low.
Figure 4. Typical Full-Coil Stepper Motor (2-Phase Type)
Terminal Block Pin Assignment
Table 6. Limit Status LED DIP Switch Settings
Axis 2 Switch Setting Operation
Active high
Active low
(factory default)
10
O
N
10
O
N
1
2
3
4
5
Phase A
Phase B
Phase A
Case Ground
Shield
Stepper Motor
Phase B

©National Instruments Corporation 17 MID-7604/7602 Power Drive User Guide
Warning The stepper motor connectors on this drive are energized when the unit is
powered on. Disconnect the MID-7604/7602 unit from the power outlet before connecting
wires to or disconnecting wires from the stepper connectors. Strip back the insulation of
the stepper wires to the stepper connectors no more than 7 mm. Failure to do so could
result in electric shock leading to serious bodily injury or death.
Use shielded, 20 AWG wire or larger for the motor power cable.
If available, you should connect a case ground wire to pin 3
(Ground/Shield) to avoid ground loops and signal noise problems.
Case ground connects to the motor housing, not to the motor power
terminals.
The MID-7604/7602 contains bipolar chopper drivers. You must wire the
stepper motors in a 4-wire configuration as shown in Figure 4. You must
isolate unused lead wires and leave them disconnected. Refer to the
Stepper Motor Configurations section of this guide for additional
information on connecting 6- and 8-wire motors and on the alternate
half-coil configuration.
Caution Never connect unused center taps or winding terminals to pin 3 (ground) or to
each other.
Encoder Terminal Blocks
For quadrature incremental encoder signals, each MID-7604/7602 axis has
a separate 8-position removable screw terminal block. Where applicable,
the MID-7604/7602 accepts two types of encoder signal inputs:
single-ended (TTL) or differential line driver. You can accommodate
open-collector output encoders by using 2.2 kΩpullup resistors to
+5 VDC.
Figure 5 shows the typical encoder wiring pin assignment for single-ended
signal input.
Figure 5. Typical Single-Ended Encoder Wiring Pin Assignment
1
2
3
4
5
6
7
8
Encoder A
Encoder B
Encoder Index
+5 V
Digital Ground

MID-7604/7602 Power Drive User Guide 18 ni.com
Figure 6 shows the typical encoder wiring pin assignment for differential
line driver signal inputs.
Figure 6. Typical Differential Line Driver Encoder Wiring Pin Assignment
If the encoder cable length is greater than 3.05 m (10 ft), use encoders
with line driver outputs for your applications. Power for a +5 V
encoder—generated by a power supply inside the MID-7604/7602—is
available on pin 7.
Note If you require other encoder power voltages, reference an external power supply to
the Digital Ground signal on the 8-pin encoder terminal block.
The MID-7604/7602 supports differential inputs for Phase A, Phase B, and
Index signals. You can easily accommodate encoders with various phase
relationships by swapping the signals and/or connecting them to the
inverting inputs as specific applications require. The Index signal must
occur when both Phase A and Phase B signals are low, as shown in
Figure 7. If the Index polarity is inverted, try reversing the Index and Index
signals on differential encoders or using the Index input on single-ended
encoders.
Figure 7 shows the proper encoder phasing for CW (forward) motor
rotation.
Figure 7. Encoder Signal Phasing, CW Rotation
1
2
3
4
5
6
7
8
Encoder A
Encoder A
Encoder B
Encoder B
Encoder Index
Encoder Index
+5 V
Digital Ground
Phase A
Phase B
Index

©National Instruments Corporation 19 MID-7604/7602 Power Drive User Guide
Closed-loop stepper applications require consistent directional polarity
between the motor and encoder for correct operation. The National
Instruments motion control standard directional polarity is as follows:
• Positive = forward = clockwise (CW) facing motor shaft
• Negative = reverse = counter-clockwise (CCW) facing motor shaft
Figure 8 shows clockwise and counter-clockwise motor rotation.
Figure 8. Clockwise and Counter-Clockwise Motor Rotation
When connecting the encoder wiring to your MID-7604/7602, use shielded
wire of at least 24 AWG. Analog noise filters filter the encoder inputs in the
MID-7604/7602. You must use cables with twisted pairs and an overall
shield for improved noise immunity and enhanced encoder signal integrity.
Figure 9 shows twisted pairs in a shielded cable.
Figure 9. Shielded Twisted Pairs
Note If you use an unshielded cable, noise can corrupt the encoder signals, resulting in
lost counts, reduced accuracy, and other erroneous encoder and controller operation.
CCW CW
Shield
+5 V
Encoder Index
Encoder Index
Encoder B
Encoder B
Encoder A
Drain
Encoder A
Digital
Ground