Measurement Computing USB-1408FS User manual

USB-1408FS
USB-based
Analog and Digital I/O Module
User's Guide
Document Revision 5, March, 2008
© Copyright 2008, Measurement Computing Corporation

3
HM USB-1408FS.doc
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the protection of the most comprehensive warranties and unmatched phone tech support. It’s the embodiment of our mission:
To provide PC-based data acquisition hardware and software that will save time and save money.
Simple installations minimize the time between setting up your system and actually making measurements. We offer quick and
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advance of the possibility of such damages.

4
Trademark and Copyright Information
TracerDAQ, Universal Library, Harsh Environment Warranty, Measurement Computing Corporation, and the Measurement
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Notice
Measurement Computing Corporation does not authorize any Measurement Computing Corporation product for use
in life support systems and/or devices without prior written consent from Measurement Computing Corporation.
Life support devices/systems are devices or systems which, a) are intended for surgical implantation into the body,
or b) support or sustain life and whose failure to perform can be reasonably expected to result in injury.
Measurement Computing Corporation products are not designed with the components required, and are not subject
to the testing required to ensure a level of reliability suitable for the treatment and diagnosis of people.

5
Table of Contents
Preface
About this User's Guide.......................................................................................................................7
What you will learn from this user's guide .........................................................................................................7
Conventions in this user's guide .........................................................................................................................7
Where to find more information.........................................................................................................................7
Chapter 1
Introducing the USB-1408FS................................................................................................................8
USB-1408FS block diagram...............................................................................................................................9
Software features................................................................................................................................................9
Connecting a USB-1408FS to your computer is easy.......................................................................................10
Chapter 2
Installing the USB-1408FS..................................................................................................................11
What comes with your USB-1408FS shipment? ..............................................................................................11
Hardware .........................................................................................................................................................................11
Additional documentation................................................................................................................................................11
Unpacking the USB-1408FS ............................................................................................................................12
Installing the software ......................................................................................................................................12
Installing the hardware .....................................................................................................................................12
Calibrating the USB-1408FS............................................................................................................................13
Chapter 3
Functional Details...............................................................................................................................14
Theory of operation - analog input acquisition modes .....................................................................................14
Software paced mode.......................................................................................................................................................14
Continuous scan mode.....................................................................................................................................................14
External components ........................................................................................................................................14
USB connector.................................................................................................................................................................15
LED .................................................................................................................................................................................15
Screw terminal wiring......................................................................................................................................................15
Main connector and pin out .............................................................................................................................................16
Analog input terminals (CH0 IN - CH7 IN).....................................................................................................................16
Analog output terminals (D/A OUT 0 and D/A OUT 1)..................................................................................................19
Digital I/O terminals (Port A0 to A7, and Port B0 to B7)................................................................................................19
Power terminals ...............................................................................................................................................................20
External trigger terminal..................................................................................................................................................20
Counter terminal..............................................................................................................................................................20
+2.5VREF terminal..........................................................................................................................................................21
SYNC terminal ................................................................................................................................................................21
Ground terminals .............................................................................................................................................................21
Accuracy...........................................................................................................................................................21
USB-1408FS channel gain queue feature.........................................................................................................24
Synchronizing multiple units............................................................................................................................24
Chapter 4
Specifications......................................................................................................................................26
Analog input.....................................................................................................................................................26
Analog output...................................................................................................................................................28
Digital input/output...........................................................................................................................................28
External trigger.................................................................................................................................................29
External clock input/output...............................................................................................................................29
Counter section.................................................................................................................................................29

USB-1408FS User's Guide
6
Non-volatile memory........................................................................................................................................30
Microcontroller.................................................................................................................................................30
Power................................................................................................................................................................30
General .............................................................................................................................................................30
Environmental ..................................................................................................................................................31
Mechanical .......................................................................................................................................................31
Main connector and pin out..............................................................................................................................31
4-channel differential mode.............................................................................................................................................31
8-channel single-ended mode...........................................................................................................................................32
Declaration of Conformity..................................................................................................................33

7
Preface
About this User's Guide
What you will learn from this user's guide
This user's guide explains how to install, configure, and use the USB-1408FS, and refers you to related
documents available on our web site, and to technical support resources.
Conventions in this user's guide
For more information on …
Text presented in a box signifies additional information and helpful hints related to the subject matter you are
reading.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
< : > Angle brackets that enclose numbers separated by a colon signify a range of numbers, such as those assigned
to registers, bit settings, etc.
bold text Bold text is used for the names of objects on the screen, such as buttons, text boxes, and check boxes. For
example:
1. Insert the disk or CD and click the OK button.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase. For
example:
The InstaCal installation procedure is explained in the Quick Start Guide.
Never touch the exposed pins or circuit connections on the board.
Where to find more information
MCC's Specifications: USB-1408FS (the PDF version of the Specifications chapter in this guide) is
available on our web site at www.mccdaq.com/pdfs/USB-1408FS.pdf.
MCC's Quick Start Guide is available on our web site at
www.mccdaq.com/PDFmanuals/DAQ-Software-Quick-Start.pdf.
MCC's Guide to Signal Connections is available on our web site at
www.mccdaq.com/signals/signals.pdf.
MCC's Universal Library User's Guide is available on our web site at
www.mccdaq.com/PDFmanuals/sm-ul-user-guide.pdf.
MCC's Universal Library Function Reference is available on our web site at
www.mccdaq.com/PDFmanuals/sm-ul-functions.pdf.
MCC's Universal Library for LabVIEW™User’s Guide is available on our web site at
www.mccdaq.com/PDFmanuals/SM-UL-LabVIEW.pdf.
USB-1408FS User's Guide (this document) is also available on our web site at
www.mccdaq.com/PDFmanuals/USB-1408FS.pdf.

8
Chapter 1
Introducing the USB-1408FS
This user's guide contains all of the information you need to connect the USB-1408FS to your computer and to
the signals you want to measure.
The USB-1408FS is a USB 2.0 full-speed, device that is supported under popular Microsoft®Windows®
operating systems. The USB-1408FS is fully compatible with both USB 1.1 and USB 2.0 ports.
The USB-1408FS features eight analog inputs, two 12-bit analog outputs, 16 digital I/O connections, and one
32-bit external event counter.
The analog inputs are software configurable for either eight 13-bit single-ended inputs or four 14-bit differential
inputs. The 16 digital I/O lines are independently selectable as input or output in two 8-bit ports. The 32-bit
counter can count TTL pulses. A SYNC (synchronization) input/output line allows you to pace the analog input
acquisition of one USB module from the clock output of another.
The USB-1408FS is powered by the +5 volt USB supply from your computer. No external power is required.
The USB-1408FS is shown in Figure 1. I/O connections are made to the screw terminals located along each side
of the USB-1408FS.
Figure 1. USB-1408FS

USB-1408FS User's Guide Introducing the USB-1408FS
9
USB-1408FS block diagram
USB-1408FS functions are illustrated in the block diagram shown here.
Screw terminal I/O connector
SPI
8
DIO
Event Counter
1 channel
(32-bit)
USB
Microcontroller
SYNC
16
USB
Full-speed
USB 2.0
Compliant
Interface
Screw terminal I/O connector
TRIG_IN
Port A
Port B
1
Analog Input
8 single-ended
(13-bit) channels
or
4 differential
(14-bit) channels
8
Analog Output
2 (12-bit) channels 2
Figure 2. USB-1408FS functional block diagram
Software features
For information on the features of InstaCal and the other software included with your USB-1408FS, refer to the
Quick Start Guide that shipped with your device. The Quick Start Guide is also available in PDF at
www.mccdaq.com/PDFmanuals/DAQ-Software-Quick-Start.pdf.
Check www.mccdaq.com/download.htm for the latest software version.

USB-1408FS User's Guide Introducing the USB-1408FS
10
Connecting a USB-1408FS to your computer is easy
Installing a data acquisition device has never been easier.
The USB-1408FS relies upon the Microsoft Human Interface Device (HID) class drivers. The HID class
drivers ship with every copy of Windows that is designed to work with USB ports. We use the Microsoft
HID because it is a standard, and its performance delivers full control and maximizes data transfer rates for
your USB-1408FS. No third-party device driver is required.
The USB-1408FS is plug-and-play. There are no jumpers to position, DIP switches to set, or interrupts to
configure.
You can connect the USB-1408FS before or after you install the software, and without powering down
your computer first. When you connect an HID to your system, your computer automatically detects it and
configures the necessary software. You can connect and power multiple HID peripherals to your system
using a USB hub.
You can connect your system to various devices using a standard four-wire cable. The USB connector
replaces the serial and parallel port connectors with one standardized plug and port combination.
You do not need a separate power supply module. The USB automatically delivers the electrical power
required by each peripheral connected to your system.
Data can flow two ways between a computer and peripheral over USB connections.

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Chapter 2
Installing the USB-1408FS
What comes with your USB-1408FS shipment?
As you unpack your USB-1408FS, verify that the following components are included.
Hardware
USB-1408FS (shown with cable)
USB cable (2 meter length)
Additional documentation
In addition to this hardware user's guide, you should also receive the Quick Start Guide (available in PDF at
www.mccdaq.com/PDFmanuals/DAQ-Software-Quick-Start.pdf). This booklet supplies a brief description of
the software you received with your USB-1408FS and information regarding installation of that software.
Please read this booklet completely before installing any software or hardware.

USB-1408FS User's Guide Installing the USB-1408FS
12
Unpacking the USB-1408FS
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the USB-1408FS from its packaging, ground yourself using a wrist strap or by
simply touching the computer chassis or other grounded object to eliminate any stored static charge.
If your USB-1408FS is damaged, notify Measurement Computing Corporation immediately by phone, fax, or e-
mail. For international customers, contact your local distributor where you purchased the USB-1408FS.
Phone: [phone] and follow the instructions for reaching Tech Support.
Fax: [phone] to the attention of Tech Support
Email: [email protected]
Installing the software
Refer to the Quick Start Guide for instructions on installing the software on the Measurement Computing Data
Acquisition Software CD. This booklet is available in PDF at www.mccdaq.com/PDFmanuals/DAQ-Software-
Quick-Start.pdf.
Installing the hardware
Be sure you are using the latest system software
Before you install your USB-1408FS, run Windows Update to update your operating system with the latest HID
and USB drivers.
To connect the USB-1408FS to your system, turn your computer on, and connect the USB cable to a USB port
on your computer or to an external USB hub that is connected to your computer. The USB cable provides power
and communication to the USB-1408FS.
When you connect the USB-1408FS for the first time, a series of Found New Hardware popup balloons
(Windows XP) or dialogs (other Windows versions) open as the USB-1408FS is detected by your computer.
It is normal for multiple dialogs to open when you connect the USB-1408FS for the first time. For additional
information, refer to the "Notes on installing and using the USB-1408FS" that was shipped with the USB-
1408FS.
The last popup balloon or dialog states "Your new hardware is installed and ready to use," and the LED on the
USB-1408FS should flash and then remain lit. This indicates that communication is established between the
USB-1408FS and your computer.

USB-1408FS User's Guide Installing the USB-1408FS
13
You can install up to two USB-1408FS units on most computers. If you need to connect more than two USB-
1408FS units to your computer, contact Tech Support by phone, fax, or e-mail:
Phone: [phone] and follow the instructions for reaching Tech Support.
Fax: [phone] to the attention of Tech Support
Email: [e-mail]

Caution! Do not disconnect any device from the USB bus while the computer is communicating with the
USB-1408FS, or you may lose data and/or your ability to communicate with the USB-1408FS.
If the LED turns off
If the LED is illuminated but then turns off, the computer has lost communication with the USB-1408FS. To
restore communication, disconnect the USB cable from the computer, and then reconnect it. This should restore
communication, and the LED should turn back on.
Allow the USB-1408FS to operate for at least 30 minutes before using the device. This warm up time is
required to achieve the specified rated accuracy of measurements.
Calibrating the USB-1408FS
The USB-1408FS is shipped fully calibrated. Calibration coefficients are stored in EEPROM. Return the device
to Measurement Computing Corporation when calibration is required. The normal calibration interval is once
per year.

14
Chapter 3
Functional Details
Theory of operation - analog input acquisition modes
The USB-1408FS can acquire analog input data in two different modes –software paced and continuous scan.
Software paced mode
In software paced mode, you can acquire one analog sample at a time. You initiate the A/D conversion by
calling a software command. The analog value is converted to digital and returned to the computer. You can
repeat this procedure until you have the total number of samples that you want from one channel.
The maximum throughput sample rate in software paced mode is system-dependent.
Continuous scan mode
In continuous scan mode, you can acquire data from up to eight channels. The analog data is continuously
acquired and converted to digital values until you stop the scan. Data is transferred in blocks of 31 samples from
the USB-1408FS to the memory buffer on your computer.
The maximum continuous scan rate of 48 kS/s is an aggregate rate. The total acquisition rate for all channels
cannot exceed 48 kS/s. You can acquire data from one channel at 48 kS/s, two channels at 24 kS/s, and four
channels at 12 kS/s. You can start a continuous scan with either a software command or with an external
hardware trigger event.
External components
The USB-1408FS has the following external components, as shown in Figure 3.
USB connector
LED
Screw terminal banks (2)
USB
connector / cable
Screw terminal
Pins 21 to 40
Screw terminal
Pins 1 to 20
LED
Figure 3. USB-1408FS external components

USB-1408FS User's Guide Functional Details
15
USB connector
The USB connector is on the right side of the USB-1408FS. This connector provides +5 V power and
communication. The voltage supplied through the USB connector is system-dependent, and may be less than
5 V. No external power supply is required.
LED
The LED on the front of the housing indicates the communication status of the USB-1408FS. It uses up to 5 mA
of current and cannot be disabled. The table below defines the function of the USB-1408FS LED.
LED Illumination
LED Illumination
Indication
Steady green
The USB-1408FS is connected to a computer or external USB hub.
Blinks continuously
Data is being transferred.
Screw terminal wiring
The USB-1408FS has two rows of screw terminals—one row on the top edge of the housing, and one row on
the bottom edge. Each row has 20 connections. Pin numbers are identified in Figure 4.
Figure 4. USB-1408FS Screw terminal pin numbers
Screw terminal –pins 1-20
The screw terminals on the top edge of the USB-1408FS (pins 1 to 20) provide the following connections:
Eight analog input connections (CH0 IN to CH7 IN)
Two analog output connections (D/A OUT 0 to D/A OUT 1)
One external trigger source (TRIG_IN)
One SYNC terminal for external clocking and multi-unit synchronization (SYNC)
One voltage output source (2.5VREF)
Five analog ground connections (AGND)
One ground connection (GND)
One external event counter connection (CTR)

USB-1408FS User's Guide Functional Details
16
Screw terminal –pins 21-40
The screw terminals on the bottom edge of the (pins 21 to 40) provide the following connections:
16 digital I/O connections (PortA0 to Port A7, and Port B0 to Port B7)
One power connection (PC+5 V)
Three ground connections (GND)
Main connector and pin out
Connector type
Screw terminal
Wire gauge range
16 AWG to 30 AWG
20 CTR 19 SYNC 18 TRIG IN 17 GND 16 +2.5VREF 15 14 D/A OUT 1 13 D/A OUT 0 12 11 10 9 8
AGND AGND CH7 IN CH6 IN AGND CH5 IN
7 CH4 IN 6 AGND 5 CH3 IN 4 CH2 IN 3 AGND 2 CH1 IN 1 CH0 IN
GND 40 GND 31 PC +5 V 30 GND 29 Port A7 28 Port B7 39 Port B6 38 Port B5 37 Port B4 36 Port B3 35 Port B2 34 Port B1 33 Port B0 32 Port A6 27 Port A5 26 Port A4 25 Port A3 24 Port A2 23 Port A1 22 Port A0 21
8-channel single-ended mode pin out
20 CTR 19 SYNC 18 TRIG_IN 17 GND 16 +2.5VREF 15 14 D/A OUT 1 13 D/A OUT 0 12 11 10 9 8
AGND AGND CH3 IN LO CH3 IN HI AGND CH2 IN LO
7 CH2 IN HI 6 AGND 5 CH1 IN LO 4 CH1 IN HI 3 AGND 2 CH0 IN LO 1 CH0 IN HI
GND 40 GND 31 PC +5 V 30 GND 29 Port A7 28 Port B7 39 Port B6 38 Port B5 37 Port B4 36 Port B3 35 Port B2 34 Port B1 33 Port B0 32 Port A6 27 Port A5 26 Port A4 25 Port A3 24 Port A2 23 Port A1 22 Port A0 21
4-channel differential mode pin out
Analog input terminals (CH0 IN - CH7 IN)
You can connect up to eight analog input connections to the screw terminal containing pins 1 to 20 (CH0 IN
through CH7 IN.) Refer to the "Main connector and pin out" diagrams above for the location of these pins.
You can configure the analog input channels as eight single-ended channels or four differential channels. When
configured for differential mode, each analog input has 14-bit resolution. When configured for single-ended
mode, each analog input has 13-bit resolution, due to restrictions imposed by the A/D converter.
Single-ended configuration
When all of the analog input channels are configured for single-ended input mode, eight analog channels are
available. The input signal is referenced to signal ground (GND), and delivered through two wires:
The wire carrying the signal to be measured connects to CH# IN.
The second wire connects to AGND.
The input range for single-ended mode is ±10 V. No other ranges are supported in this mode. Figure 5
illustrates a typical single-ended measurement connection.

USB-1408FS User's Guide Functional Details
17
Pin 3
AGND
Pin 1
CH0
Figure 5. Single-ended measurement connection
Battery voltage should read as expected when the hardware is configured for single-ended mode.
Single-ended measurements using differential channels
To perform a single-ended measurement using differential channels, connect the signal to "CHnIN HI" input,
and ground the associated "CHnIN LO" input.
Differential configuration
When all of the analog input channels are configured for differential input mode, four analog channels are
available. In differential mode, the input signal is measured with respect to the low input.
The input signal is delivered through three wires:
The wire carrying the signal to be measured connects to CH0 IN HI, CH1 IN HI, CH2 IN HI, or CH3 IN
HI.
The wire carrying the reference signal connects to CH0 IN LO, CH1 IN LO, CH2 IN LO, or CH3 IN LO.
The third wire connects to GND.
A low-noise precision programmable gain amplifier (PGA) is available on differential channels to provide gains
of up to 20 and a dynamic range of up to 14-bits. Differential mode input voltage ranges are ±20 V, ±10 V,
±5 V, ±4 V, ±2.5 V, ±2.0 V, ±1.25 V, and ±1.0 V.
In differential mode, the following two requirements must be met for linear operation:
Any analog input must remain in the −10V to +20V range with respect to ground at all times.
The maximum differential voltage on any given analog input pair must remain within the selected voltage
range.
The input [common-mode voltage + signal] of the differential channel must be in the
−10 V to +20 V range in order to yield a useful result. For example, you input a 4 V pp sine wave to CHHI, and
apply the same sine wave 180° out of phase to CHLO. The common mode voltage is 0 V. The differential input
voltage swings from 4 V−(−4 V) = 8 V to (−4 V) − 4 V = −8V. Both inputs satisfy the
−10 V to +20 V input range requirement, and the differential voltage is suited for the ±10 V input range (see
Figure 6).

USB-1408FS User's Guide Functional Details
18
+4V
-4V
+4V
-4V
0V
CHLO
CHHI
+/-8V
8V Differential
Measured Signal
Figure 6. Differential voltage example: common mode voltage of 0 V
If you increase the common mode voltage to 11 V, the differential remains at ±8 V. Although the [common-
mode voltage + signal] on each input now has a range of +7 V to +15 V, both inputs still satisfy the −10 V to
+20 V input requirement (see Figure 7).
+11V
+7V
+11V
+/-8V
+15V
8V Differential
CHLO
CHHI
Measured Signal
Figure 7. Differential voltage example: common mode voltage of 11 V
If you decrease the common-mode voltage to −7 V, the differential stays at ±8 V. However, the solution now
violates the input range condition of −10 V to +20 V. The voltage on each analog input now swings from −3V
to −11V. Voltages between −10 V and −3 V are resolved, but those below -10 V are clipped (see Figure 8).
-3V
-11V
-7V
+/-7V
8V Differential
-11V
-7V
-3V
3V
CHLO
CHHI
Measured Signal
Figure 8. Differential voltage example: common mode voltage of -7 V
Since the analog inputs are restricted to a −10 V to +20 V signal swing with respect to ground, all ranges except
±20V can realize a linear output for any differential signal with zero common mode voltage and full scale signal
inputs. The ±20 V range is the exception. You cannot put −20 V on CHHI and 0 V on CHLO since this violates
the input range criteria. The following table shows some possible inputs and the expected results.

USB-1408FS User's Guide Functional Details
19
Sample inputs and differential results
CHHI
CHLO
Result
−20 V
0 V
In Valid
−15 V
+5 V
In Valid
−10 V
0 V
−10 V
−10 V
+10 V
−20 V
0 V
+10 V
−10 V
0 V
+20 V
−20 V
+10 V
−10 V
+20 V
+10 V
0 V
+10 V
+15 V
−5 V
+20 V
+20 V
0
+20 V
For more information on analog signal connections
For more information on single-ended and differential inputs, refer to the Guide to Signal Connections (this
document is available on our web site at www.mccdaq.com/signals/signals.pdf)
Analog output terminals (D/A OUT 0 and D/A OUT 1)
You can connect up to two analog output connections to the screw terminal pins 13 and 14 (D/A OUT 0 and D/A
OUT 1). Refer to the "Main connector and pin out" diagrams on page 16 for the location of these pins.
Each channel can be paced individually at rates up to 10,000 updates per second. Both channels can be paced
simultaneously using the same time base at 5000 updates per channel. The 0-4.096 V output range provides a
convenient 1 mV per LSB when setting the output voltage levels.
Digital I/O terminals (Port A0 to A7, and Port B0 to B7)
You can connect up to 16 digital I/O lines to the screw terminal containing pins 21 to 40 (Port A0 to Port A7,
and Port B0 to Port B7.) Refer to the "Main connector and pin out" diagrams on page 16 for the location of
these pins. You can configure each digital port for either input or output.
When you configure the digital bits for input, you can use the digital I/O terminals to detect the state of any
TTL level input. Refer to the switch shown in Figure 9 and the schematic shown in Figure 10. If the switch is
set to the +5 V input, Port A0 reads TRUE (1). If you move the switch to GND, Port A0 reads FALSE.
Pin 21
PORT A0
Pin 30
PC +5V
Pin 40
GND
Figure 9. Digital connection Port A0 detecting the state of a switch

USB-1408FS User's Guide Functional Details
20
+5V+GND
Port A0
Figure 10. Schematic showing switch detection by digital channel Port A0
For more information on digital signal connections
For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal
Connections (available on our web site at www.mccdaq.com/signals/signals.pdf).
Power terminals
The PC +5V connection (pin 30) draws power from the USB connector. This terminal is a 5 V output that is
supplied by the host computer. Refer to the "Main connector and pin out" diagrams on page 16 for the location
of this pin.
Caution! The +5 V terminal is an output. Do not connect to an external power supply or you may damage
the USB-1408FS and possibly the computer.
The maximum total output current that can be drawn from all USB-1408FS connections (power, analog and
digital outputs) is 420 mA. This maximum applies to most personal computers and self-powered USB hubs.
Bus-powered hubs and notebook computers may limit the maximum available output current to 100 mA.
Just connecting the USB-1408FS to your computer draws 80 mA of current from the USB +5 V supply. Once
you start running applications with the USB-1408FS, each DIO bit can draw up to 2.5 mA, and each analog
output can draw 15 mA. The maximum amount of +5 V current available for experimental use, over and above
that required by the USB-1408FS, is the difference between the total current requirement of the USB (based on
the application), and the allowed current draw of the PC platform (500 mA for desktop PCs and self-powered
hubs, or 100 mA for bus-powered hubs and notebook computers). With all outputs at their maximum output
current, you can calculate the total current requirement of the USB-1408FS USB +5 V supply as follows:
(USB-1408FS @ 80 mA) + (16 DIO @ 2.5 mA ea) + (2 AO @ 15 mA ea ) = 150 mA
For an application running on a PC or powered hub, the maximum available excess current is
500 mA −150 mA = 350 mA. This number is the total maximum available current at the PC +5 V screw
terminals. Measurement Computing highly recommends that you figure in a safety factor of 20% below this
maximum current loading for your applications. A conservative, safe user maximum in this case would be
280 mA.
Since laptop computers typically allow up to 100 mA, the USB-1408FS in a fully-loaded configuration may be
above that allowed by the computer. In this case, you must determine the per-pin loading in the application to
ensure that the maximum loading criteria is met. The per-pin loading is calculated by simply dividing the +5 V
by the load impedance of the pin in question.
External trigger terminal
The TRIG_IN connection (pin 18) can be configured for either rising or falling edge. Refer to the "Main
connector and pin out" diagrams on page 16 for the location of this pin.
Counter terminal
The CTR connection (pin 20) is input to the 32-bit external event. Refer to the "Main connector and pin out"
diagrams on page 16 for the location of this pin. The internal counter increments when the TTL levels transition
from low to high. The counter can count frequencies of up to 1 MHz.