Ddc Tr122 User manual

TR122 CPCI MODULE

2 CHANNEL 100 MHz, 200 MS/S

TRANSIENT RECORDER

January 2005

Data Design Corporation

7851-A Beechcraft Avenue

Gaithersburg, MD 20879

WWW.DATADESIGNCORP.NET

(301) 670-1157

CONTENTS

1.0 Introduction ............................................................................................................... 3

1.1 Specifications Summary ....................................................................................... 4

1.2 Setup and Installation ........................................................................................... 5

1.3 Front Panel ........................................................................................................... 6

2.0 Using TR122 Software .............................................................................................. 7

2.1 Customizing The Display ....................................................................................... 8

2.2 Oscilloscope Mode ................................................................................................ 9

2.2.1 Vertical Settings .............................................................................................. 9

2.2.2 Horizontal Settings ........................................................................................ 10

2.2.3 Trigger Settings............................................................................................. 11

2.2.4 Saving Waveforms And Settings................................................................... 13

2.3 Transient Recorder Mode .................................................................................... 14

2.3.1 Configuring Transient Record Memory ......................................................... 15

2.3.2 Performing A Transient Recording................................................................ 17

2.3.2 Saving A Transient Record ........................................................................... 18

3.0 TR122 Software Source Code ................................................................................ 20

3.1 TR122 Software Architecture............................................................................... 21

3.2 The TR122 API.................................................................................................... 23

3.2.1 Calibration Functions .................................................................................... 25

3.2.2 Abstract Instrument Functions....................................................................... 26

3.2.3 Display Functions.......................................................................................... 28

3.2.4 The Auto Thread ........................................................................................... 30

4.0 Calibration ............................................................................................................... 31

4.1 Using Calibration Features Of The TR122 Software............................................ 32

4.1.1 Analog Frequency Compensation Alignment ................................................ 33

4.1.2 Stored Calibration Controls ........................................................................... 34

4.1.3 Adjusting The Calibration Data...................................................................... 35

1.0 Introduction

The TR122 is a high performance two channel transient waveform digitizing instrument

designed in a single slot CPCI module and capable of digitizing to 12 bits at rates up to 200

million samples per second (MS/s) on both channels. Each channel includes an independent

analog front end and analog-to-digital converter providing superior interchannel isolation and

full bandwidth availability on all channels. The TR122 segmented memory architecture and

internal timer allow multiple sequential events to be captured and time stamped without the need

to read data between events. A two million sample static memory is provided for each channel

and is divisible into smaller data segments.

The TR122 analog inputs have nine 1 volt to 500 volt full scale ranges selectable in 1,2,5

steps. A full scale input offset adjustment is also available. The effective sample rate is

adjustable from 1 MS/s to 200 MS/s in eight steps. Each TR122 unit is always an independent

instrument, but can coexist in hardware and software with additional units and other instruments

in the same CPCI system.

The TR122 can respond to trigger events from either channel, from an external trigger

input, or from software. A trigger event stops the continuous recording of a circular buffer of

samples when a specified number of samples after the trigger have been recorded. The number

of samples recorded after the trigger is adjustable. This approach allows the user to select an

appropriate number of pre trigger samples to be left in memory when the record is complete.

A binary status recorded with the data indicates whether each sample was taken before or after

the trigger event. The TR122 software automatically sorts the data to chronological order,

making the intricate details of the records transparent to the user.

The sample memory can be segmented in multiples of 64K samples. A 32-bit (4 billion

count) internal timer is used to record a count with each trigger event which can be used to

determine the relative time of multiple trigger events with microsecond accuracy. These time

stamps are saved in a first-in-first-out (FIFO) memory which can be accessed through the TR122

software to determine how many triggers events are present in the sample memory and when

they occurred with respect to each other.

While the TR122 is not an oscilloscope, the software is designed with much of the look

and feel of an oscilloscope for the benefit of instant user familiarity. The instrument and

connected devices can be configured in an oscilloscope mode and then switched to transient

recorder mode to take advantage of powerful transient recorder features.

Finally, the TR122 software source code is provided as open source. In a world of data

acquisition now muddied by thousands of semi-standard and custom solutions it makes sense

to provide a properly layered design accessible to the user for unique needs. The principles of

the software design are defined in this manual and are intended to allow the advanced user to

peel back the layers and snap in other front end software. Such efforts are always underway

and popular additions will be published on the Data Design website as they become available.

1.1 Specifications Summary

Dataway Interface Ambient Temperature Range

Compact PCI at 32 Bits and 33 MHz 0 To 70 C

Compliant with PICMG 2.0 R3.0

Single Width 3U Compact PCI Card

SampleRate Memory

200 MS/s All Channels 2 MSample Per Channel

100 MHz Bandwidth 64 KSample Minimum Block Size

ConfigurableSegmenting

Input Channel Architecture Input Sensitivity

2 Independent Analog Signal Inputs 12-Bit Resolution

1 External Trigger Input 1-500 Volts Full Scale In 9 Ranges

0.05% Accuracy (10 LSB)

80 dB Minimum Interchannel Isolation

Analog Input Characteristics Input Withstand Rating

Single Ended DC Or AC Coupled 1 MΩInput ±250 VDC

Full Scale Offset 10-Bit Resolution 50 ΩInput 4 Watts (14 Volts RMS)

1 MΩ20 pF Or 50 ΩImpedance

External Trigger Input Trigger Input Sources

Single Ended DC Coupled Channel Greater Than Full Scale Range

1 KΩ20 pF External

±10V 10-Bit Resolution

Rising Or Falling Edge

1.2 Setup and Installation

The TR122 is a single width 3U CPCI module. To insert the TR122 in the CPCI crate,

choose any convenient slot and slide the module into the crate with its top and bottom mated to

the guide rails. Be sure that the module is properly aligned with the connector at the back of the

crate. Push the module toward the back of the crate with gentle pressure. When the card pushes

back, push the locking lever down and press the card firmly into the crate with firm pressure on

the top and bottom of the front panel. The locking lever will raise and lock into place. Fasten

the retaining screws at the upper end of the front panel and at the bottom of the front panel below

the lever. To remove the card, reverse the process by removing the retaining screws and pressing

down firmly on the locking lever to disengage the card from the connector at the rear

of the crate.

NOTE: The module should be inserted in the crate only after turning off the power

to the crate. Otherwise, damage to the module or system is possible due to momentary

misalignment of pins on the connector. CPCI hot swap operation is not supported.

It is recommended that the TR122 module and a controller be installed alone in

the crate until the user is familiar with TR122 operation enough to integrate it with other

modules in an instrumentation system. When the TR122 is installed in a slot where it has not

been before, the CPCI system will detect it as a new device at which point it will need access to

driver software. The software supplied with the TR122 is designed to operate on platforms with

Microsoft Windows 2000 and newer operating systems. To install drivers on these systems,

point the installation wizard to the location of the included CD. A CD drive may be located on

the crate controller or it may be mounted over a network connection using the wizard’s “specify

a location” option. The files the installation wizard will need are located in the root directory of

the CD. Follow the steps displayed by the installation wizard at the end of which the wizard

should indicate that a “TR122 Transient Recorder” has been installed.

To install the TR122 software, use the Windows explorer or similar tool to locate the

software CD. Point to the directory on the CD identified as \TR122\Install. Run the program

SETUP.EXE and follow the on screen instructions for the familiar software installation process.

When any new software has just been installed, it is usually best to reboot the crate controller

before attempting to use the software, even when this is not strictly necessary. At this point the

installation is complete and the TR122 and turnkey software are ready to be used.

1.3 Front Panel

The TR122 front panel provides three standard BNC connections to the instrument

electronics. These are labeled for the two channels and the external trigger. There is also a serial

number label on the card ejector lever. This number will be presented by the TR122 software to

indicate which TR122 is being used, which may be important when there are multiple such

instruments in the system.

While the instrument has some immunity from typical connection mistakes, care should

be still used when connecting external devices. Always observe the maximum ratings indicated

in the specifications. Also note that some of these ratings indicate particular settings. For

example, the 50 ohm termination is only capable of handling 4 watts, thereby limiting the

peak voltage that can be handled with this setting.

The external trigger input is limited to +/-10V peak. While slightly higher voltages will

not damage the unit, they will operate a protection mechanism. It is recommended that care be

taken to keep this input within its specified range. This input is typically used to provide an

effective third input which may carry only binary trigger information or to provide some ability

to synchronize multiple instruments.

2.0 Using TR122 Software

The TR122 comes with a turnkey software package which allows the user to quickly take

advantage of all instrument features in a standalone configuration. This software is designed to

coexist with other instruments as well as to allow multiple TR122 instruments to be installed and

operated in the same CPCI crate. Installation of the software is discussed in section 1.2 above.

The software is designed to have the look and feel of an oscilloscope to take advantage of user

familiarity with such instruments, while supporting features unique to a transient recorder. This

discussion assumes that the user is familiar with the operation of an oscilloscope.

Upon starting the TR122 software, a splash screen will be displayed while the software

searches for and configures a TR122 device in the system. The software will locate a TR122

which is not already in use and complain if one can not be found. Assuming a TR122 is found, a

clicking of relays can be heard as the software configures the unit to default settings. The control

panel screen shown in Figure 2.1 will appear and its title bar will indicate the serial number of

the TR122 which is being operated. This serial number corresponds to that found on the card

ejector lever of the instrument. To reconnect this instance of the control panel to another TR122

instrument in the system use the Select item under the Device menu. The software prevents more

than one control panel instance from addressing a single TR122 instrument.

Figure 2.1 TR122 Control Panel

The TR122 starts in the oscilloscope mode and returns to default settings for all controls.

This will also be the case any time a new card, or the same card, is found using the Select menu

item. This gives the user a practical starting point from which to configure the measurement

environment. With the factory default display configuration, a real time display of data from

both channels will immediately appear in the oscilloscope window and a vertical white line will

indicate the time location of the trigger event for each record.

2.1 Customizing The Display

Data from the TR122 are displayed in an oscilloscope display format. The colors and

amounts of information displayed can be adjusted with a high degree of freedom. It is useful

to review the configuration at this point to become familiar with what is being displayed.

To configure the display, double click the left mouse button on the oscilloscope screen. The

dialog window in Figure 2.2 will appear. Changing any item in the dialog will immediately

affect the display.

Figure 2.2 Display Configuration Dialog

The Display Items list represents all of the information which can be displayed on the

oscilloscope screen. The check boxes indicate which items are being displayed and the color

bars are the colors in which they are being displayed. Some items can be removed from the

display. For example, to view only one channel simply uncheck the other channel by clicking on

the check box. To change the color, click on the color bar for an item to display a standard color

selection dialog. Clearly, if the background and the gradicule are the same color, the gradicule

will effectively disappear. The same would be true for any other item.

The options list allows for selection of optional display features. The Show Tick Marks

control toggles the display of the tick marks on the center gradicule lines. Draw Lines Betweens

Samples places a best fit line between each sample on the screen making the display bright and

easy to read. In some cases it may be advantageous to see the discrete sample points by

unchecking this option.

Use Save As Defaults to cause these settings to be loaded each time the software is

started. These settings are saved in a file called TR122disp.cfg in the same directory as the

software executable. This file is not human readable. To restore the factory defaults, this file

should be deleted. The Restore Defaults button will cause the contents of this file to be loaded or

the factory defaults will be loaded if this file is not present. The Ok button just closes the dialog.

2.2 Oscilloscope Mode

Keep in mind that a transient recorder is not an oscilloscope. Although the TR122

software makes a valiant effort at imitating an oscilloscope, the user is bound to be disappointed

in comparison to instruments designed for this purpose. A transient recorder is somewhat like a

deep memory oscilloscope restricted to operate in the single shot trigger mode. The TR122

oscilloscope mode uses an independent software thread to record and display transient records

of the entire two million sample memory at a rate dependant on the selected horizontal time base.

To achieve slower timebases the software must lower the sample rate and compress the data. At

faster horizontal settings this is fairly undetectable, while at slower settings the transient recorder

characteristics can be seen as full memory records are collected and displayed. On the other

hand, significant time frames of data are always available, making it easier to capture activity

well before or after the trigger.

The oscilloscope mode is intended to be used to establish the settings required to perform

a transient measurement. Vertical and horizontal selections along with trigger source selections

have an immediate effect on how the data is being acquired and displayed. The user is likely

familiar with most of the controls and settings provided. The typical vertical, horizontal, and

trigger menus of an oscilloscope are accessed by clicking the tabs at the upper left of the

window. The following discussion provides some additional insight into how these controls

are used.

2.2.1 Vertical Settings

The vertical controls for each channel are under the tabs marked CH1 and CH2 as shown

in Figure 2.1 above. The oscilloscope screen in any mode always displays only 8-bits of the

12-bit data stream provided by the TR122. The Volts/Div 8-Bit setting assumes that the software

will be concerned with only the upper 8 bits. Of course, when data are eventually saved to disk

in transient mode, all 12 bits will always be represented.

To allow the user to examine what is happening within the lower bits, the software

provides a setting called Bit Mag. This can magnify the image to 1,2,4,8,or16 by sliding the

visible bits down the sample by 0 to 4 bits. It should be noted that the offset and trigger settings

are calibrated to be valid with the 8-bit display and will not be coherent with the Bit Mag set to

greater than 1. The volts per division display below the oscilloscope screen will always display a

value taking the Bit Mag into account. The volt per division display at either location can be

used to adjust the front end attenuator of the TR122.

All controls in the TR122 software can be adjusted by clicking on them with the mouse

buttons. For most, though not all, controls the left mouse button will increase the value

of the control and the right mouse button will return its value.

The coupling, input impendence, and probe settings are as they would be on an

oscilloscope. The probe setting has no physical effect on the instrument, but simply multiplies

the displayed values for volts per division for ease of use when an oscilloscope probe is

connected to the instrument.

The analog offset is typically adjusted as part of the vertical controls of an oscilloscope,

known generally as vertical position. With a transient recorder it is more typical to discuss

offset. The term offset will be used in the context of the TR122. The offset allows a DC value

to be added to the input signal, typically to bring a signal with a DC offset within range of the

instrument; but also to allow for separation of multiple signals on a display, such as would be a

typical use of an oscilloscope vertical position control. Within TR122 software the offset is

controlled directly on the screen with the mouse. The arrow icons at the left of the screen

indicate where the offset is for each channel by color. Move the mouse cursor to the left most

horizontal division of the oscilloscope screen and click the left mouse button to move the offset

for the nearest channel to the screen position of the mouse. Holding the left mouse button and

moving the mouse will drag the location of the offset. The position of the icon represents the

display location of a zero volt DC signal input. The data behind the value, such as that stored to

disk, will include the DC offset.

2.2.2 Horizontal Settings

Selecting the HORIZ tab in the controls dialog at the left of the oscilloscope screen will

display the horizontal settings controls as shown in Figure 2.3 below. In oscilloscope mode the

horizontal Sec/Div control is the only enabled control. This control is similar to the control of

the same name on an oscilloscope. The setting can also be adjusted by clicking on the status line

copy of this value located below the oscilloscope screen.

Figure 2.3 TR122 Control Panel Horizontal Controls

The horizontal menu includes a status display value in Time At Mid Screen. This box

will display the time represented at the horizontal center line of the gradicule with respect to the

trigger location. The units and resolution will depend on the Sec/Div setting and the magnitude

of the value. This display can be quite useful when the trigger location is not displayed or is

beyond the horizontal bounds of the screen. Because the full size of the memory is quite large,

it is possible to view events substantially on either side of the trigger and know where they are in

time. This feature is available in transient recorder mode as well. For oscilloscope users, this

feature starts to show the strengths of a transient recorder design for certain types of

measurements within the same price/performance class of instrument.

The horizontal location at which the trigger bar is displayed can be adjusted by clicking

and holding the left mouse button on the display and dragging the display in either direction.

The position can also be adjusted in steps with the < and > buttons at the bottoms of the screen.

These controls are similar to the horizontal position control of an oscilloscope.

The horizontal menu in the oscilloscope mode also shows the ghosted values of the

transient recorder settings being used. The memory geometry will be constant in oscilloscope

operation, but the sample rate will change with certain ranges of the Sec/Div setting. This

display can be useful in determining what sample rate setting may be required to perform

transient measurements on a given input.

2.2.3 Trigger Settings

Selecting the TRIG tab in the controls dialog at the left of the oscilloscope screen will

display the trigger settings controls as shown in Figure 2.4 below.

Figure 2.4 TR122 Control Panel Trigger Controls

In oscilloscope mode the trigger controls mirror those on an oscilloscope. The trigger

Source can be either channel or the external trigger input. The trigger Slope can be rising or

falling edge. The trigger system can operate in a Mode of AUTO, NORMAL, or SINGLE which

mirror their oscilloscope equivalents. The NORMAL mode will record and display new

information only after receiving a trigger event and again after each subsequent trigger event

following complete display of the data from the previous event. The SINGLE mode will display

information only from the first such event after which the Run/Stop control in the lower right

corner of the screen will be set to STOP. Data from an additional trigger event can only be

recorded by clicking on the Run/Stop control to set it back to RUN. The AUTO mode behaves like

the NORMAL mode except that the software will inject a trigger if one is not received in an

internally determined time. This trigger will of course not be synchronous with any event in the

input signal but the resulting display can be useful in the event that it is not clear how the trigger

source should be prepared. If a trigger event does occur before the internal timeout on each

cycle, the display will be properly synchronized to this event.

The Run/Stop control can be set to STOP in any trigger mode to cause the software to

ignore any additional trigger events. The display will be a static representation of the last

captured data. When the trigger system is set to STOP in the oscilloscope AUTO or NORMAL

modes, only the data already on the screen will be available. When the SINGLE trigger mode sets

the control to STOP, the entire memory is available for review. This distinction relates to the

ongoing recording operations in the other modes. That is, the SINGLE mode does not record pre

trigger samples for an anticipated subsequent trigger while the other modes do, which would of

course overwrite data from any previous trigger. When switching between trigger modes, the

Run/Stop control is automatically returned to RUN to avoid the typical need to do this manually.

The analog voltage threshold at which a trigger is detected is called the trigger level. For

the external trigger input, this level is adjustable in an absolute range of –10V to +10V using the

Ext Level control. If the trigger source specifies that one of the channels should be used, the

range becomes somewhat larger than the full scale analog input range. The location of the

trigger threshold will be indicated in an abstract way with an arrow on the right side of the

oscilloscope display with the color of the selected source channel. The level can be adjusted by

clicking the left mouse button on the oscilloscope screen within the far right horizontal division.

The trigger threshold will be moved to the location of the mouse cursor. The location can be

dragged by holding the left mouse button down while moving the mouse. If the offset were to be

adjusted, the trigger location will be further adjusted with it to keep the intended trigger

threshold with respect to the new zero volt line. This may force the trigger location off the

screen, which will be indicated by a vertical pointing arrow at the far left top or bottom of the

screen. This is the benefit of a trigger range greater than the full scale analog input range.

The Force Trigger button allows the user to issue a software trigger at any time in any

mode. This function is independent of anything else in the software. If the instrument and

software are configured to respond to a trigger, clicking this control will cause it to act the same

as if the trigger had come from the specified source. Of course there is no way to synchronize

this action to any event, but this control can be useful in performing setup operations,

particularly in transient recorder mode.

Finally, the Center Trigger button automatically returns the display settings so that the

trigger event is displayed at the horizontal center line of the gradicule. This can be useful when

exploring the outer reaches of the recorded time in any mode and it is desired to return to time

zero, the time of the trigger event.

2.2.4 Saving Waveforms And Settings

In the oscilloscope mode there is generally not a known set of data in memory, except

perhaps as the result of a single shot trigger operation. The transient recorder mode handles the

recording to known data sets in memory somewhat like a sophisticated single shot trigger

operation. Therefore, saving of sample data to disk is not supported in oscilloscope mode.

However, there is always a waveform image on the display and saving this image to disk is

supported. Select the menu item Save Image in the File menu. A standard file dialog will ask

for a file name under which to store a bitmap image of the oscilloscope display. This bitmap can

be used in any document such as shown in Figure 2.5 below. When the image is saved to disk,

the Run/Stop control is set to STOP. If the control was set to RUN, it is returned to RUN when the

file save is complete. This time will be very brief.

Figure 2.5 Captured TR122 Oscilloscope Screen Image

Generally, the oscilloscope mode is used to setup the TR122 instrument for transient

recording operations. Some setting can not even be changed once transient recorder mode is

entered. For this reason, if settings are to be saved to disk to preserve a given setup, the

oscilloscope mode would be the right place to do it. The menu items Save Settings and Load

Settings are available in the File menu in the oscilloscope mode. The Save Settings item will

prompt for a file name under which to save the current settings of the user controls. When the

TR122 software is started, default settings are always installed. Stored settings can be retrieved

using the Load Settings menu item.

2.3 Transient Recorder Mode

Changing between oscilloscope and transient recorder mode is performed by selecting a

mode from the Mode menu item. This menu indicates the current mode with a check mark.

Starting the transient recorder mode will result in a blank display screen and the Run/Stop control

indicating STOP. The status display of Sec/Div will be missing as this value does not have

meaning until a recording is made and displayed.

The vertical controls under CH1 and CH2 perform the same as they do in the

oscilloscope mode. The trigger controls under TRIG also perform much the same except that

the trigger modes of the oscilloscope do not have any meaning in transient recorder mode. As a

result the trigger Mode control is disabled.

The offset and channel source trigger level controls are not adjustable in the transient

recorder mode. These settings are generally adjusted while the user has a good look at incoming

data in the oscilloscope mode and then are not to be changed while a transient measurement is

taken. All other controls can be adjusted. However, adjusting any control will invalidate any

previous transient record and the display screen will be cleared. It is important to recognize that

a transient record is a once and done event with a very specific set of parameters on the

instrument. By operating in this manner, the user can be sure that any transient records displayed

or written to disk were in fact taken with the settings shown. In contrast, the oscilloscope mode,

which also clears the screen on a setting change under most conditions for the same reason, will

generally refresh the data with a new record following shortly after the setting change. The

transient recorder mode requires user intervention to collect and display each record.

2.3.1 Configuring Transient Record Memory

Beyond the basic setup which matches that of an oscilloscope, configuring the transient

recorder mode involves selecting a sample rate and memory geometry. Defining this

information is a rather manual step which is unique to a transient recorder, but it allows the user

to control and be aware of specific parameters of the recording. These parameters are critical

knowledge for some types of measurements and are generally not reported by an oscilloscope.

To allow control of these parameters, the HORIZ tab control in transient recorder mode will

appear as in Figure 2.6 below.

Figure 2.6 TR122 Memory Geometry Controls

The all important Sample Rate control is self explanatory to transient recorder users.

This control will generally be adjusted based on the frequency characteristics of the input signal

being viewed and by trading off recorded signal detail with the length of time which can be

stored in the instrument sample memory. When selecting a sample rate (measured in MHz or

Million Samples Per Second (MS/s)), keep in mind that the bandwidth of the TR122 analog

circuitry is always 100 MHz, and the roll off of the pass band is not steep. Any incoming signal

with a frequency component greater than half the sample rate can potentially appear misleading

when displayed due to aliasing, an important digital signal processing mathematical concept

which must be understood for successful use of a transient recorder or a digital oscilloscope.

Because the input bandwidth is 100 MHz, the potential for aliased information in the display is

limited when the full 200 MS/s sample rate is used. However, the effect can become pronounced

at lower sample rates.

The time recorded in memory will be equal to the number of samples stored in memory

(samples) divided by the sample rate (samples/second). The full depth of the memory is two

million samples. Therefore, at the full sample rate of 200 MS/s the memory will hold

2M/200MS/s or 0.01 seconds of time. At the slowest sample rate of 1 MS/s this expands to 2

seconds of time. The user is probably aware that both times can be considered fairly long

transient events.

In some cases it may not be necessary to record so much time. It may also be the case

that several events are expected to occur in rapid succession. It is possible to configure the

TR122 memory to capture multiple trigger events by dividing its full memory into smaller

segments. The Segment Size is measured in thousands of samples (K samples). The smallest

available segment size can be referred to as a block of memory. The block size of the TR122 is

64K samples. Note that all dimensions suffer from the binary number system employed by the

modern computer, so block and segment sizes will be powers of 2. For example, 64K samples

is 65536 samples. A segment in the TR122 can be sized as a power of 2 times the block size, up

to the size of the full memory. That is, the segment size can be selected as 64K, 128K, 256K,

512K, 1024K, or 2048K samples. The memory can therefore be divided into 32, 16, 8, 4, 2,

or 1 segments respectively. Thus, for short rapidly occurring transient events, up to 32 such

events can be stored in memory before the data must be read or a new recording started.

When a recording is started, the TR122 will immediately begin recording data in the first

segment of memory, filling the segment with samples and returning to the beginning of the

segment to start again in a continuous loop. When a trigger event is detected, the TR122 will

begin counting samples to be recorded after the trigger event, as defined by the user in the

control Post Trigger Samples. When this number of samples has been recorded, the TR122

moves on to the next segment and begins again recording pre trigger samples.

Clearly for sample data in this circular buffer architecture to be sensible, the segment

must be fully written with pre or post trigger samples related to the trigger event. To guarantee

that this happens, the TR122 will not be sensitive to a trigger event until the segment has filled at

least once with pre trigger samples. Once a trigger is received, the TR122 will not be sensitive to

another trigger until all post trigger samples have been recorded and the next segment has been

filled with pre trigger sample data. Therefore, the minimum time between trigger events will be

defined by the memory geometry selected as

Minimum time between trigger events = (segment size / sample rate) + (post trigger samples / sample rate)

Internally to the TR122 software and hardware, the number of Post Trigger Samples can

be defined to any multiple of 2. However, this resolution is rarely needed. The TR122 control

panel allows the Post Trigger Samples control to be adjusted in steps of 512 samples. The limits

will require there to remain at least 1K (1024) pre trigger samples and at least 1K post triggers

samples within the segment. When selecting a segment size, the Post Trigger Samples control is

automatically adjusted to half the segment size. The shortcut buttons under the control allow

setting commonly used values for Post Trigger Samples with one click.

2.3.2 Performing A Transient Recording

To prepare the TR122 to capture a transient record, set the Run/Stop control to RUN. At

that point the memory geometry controls are frozen and the TR122 begins recording pre trigger

samples and waiting for a trigger event. The other controls remain available to the user, however

it should be kept in mind that adjusting controls after the first trigger is received could cause an

inconsistency in the data between one segment and the next.

The TR122 will continue to record data until enough trigger events have occurred to fill

all segments, at which point it will automatically stop recording and display the data from the

first segment. To stop the recording and display data before all segments have been filled,

manually set the Run/Stop control to STOP. The data from the first segment will be displayed

on the oscilloscope screen with the trigger event at the center of the gradicule.

When a transient record is displayed, the dark bar below the display will be filled with

red and green bands. This bar is referred to as the sample memory profiler. The green band

covers the portion of the memory which is filled with valid samples. The red band lays over top

of the green band and indicates which segment of memory is currently being displayed. The size

of these bands is relative to the segment size, and of course for geometry consisting of a single

full memory segment, the sample memory profiler will be entirely red. This display provides a

clear visual indication of how many trigger events were received in a transient record, the

relative size of the data for each segment, and which trigger event is being examined. Figure 2.7

below shows the display of a transient record in which four trigger events filled 64K segments

before the record was discontinued by the user. The second segment is displayed.

Figure 2.7 Displaying A Transient Record

When a transient record is being displayed, the software will generate a seconds per

division status indication in its traditional place. This number is not adjustable. While the

oscilloscope mode is designed to compress or expand samples on the screen to reach a specific

time gradicule, the transient recorder mode strictly presents 25 samples per division. It is

intended to be crystal clear what the pure sample data looks like when graphed at one vertical

axis point to one horizontal axis point. Therefore, the seconds per division value will only

change based on the sample rate of the transient record.

An additional time point is displayed on the status bar along with the seconds per

division. This is the absolute time at which the trigger event for the currently displayed segment

occurred with respect to the first trigger event, based on a microsecond counter in the TR122.

The display of the first trigger event will always show zero microseconds (0uS) in this location.

Of course, the timer could lapse during a transient record and thereby provide strange results, but

it is good for over an hour – an eternity in the world of transient recording.

To move the display between segments use the << and >> buttons on either side of the

sample memory profiler. This action will set the display to show the trigger location of the new

segment at the center of the gradicule. To move the trigger location and explore the reaches of

the memory segment before or after the trigger, use the same mouse screen control or the < and >

buttons as in the oscilloscope mode display. The Time At Midscreen display under the HORIZ

tab will represent the time at the middle of the display gradicule with respect to the trigger event

in the currently displayed segment.

2.3.2 Saving A Transient Record

The sample data in a transient record can be saved in one of three formats. The current

displayed image can be saved as a bitmap as in the oscilloscope mode, or the data can be saved

in binary or comma separated text format. A bitmap image may be useful for a brief report about

a recorded signal. The binary format would typically be used by some form of custom post

processing software. The text form is somewhat human readable or it may be used for

processing in spreadsheets or other standard post processing software.

Saving a bitmap image follows the same procedure discussed for the oscilloscope mode.

Saving data is completed using the Save Data item under the File menu. This item is only

available in transient recorder mode. It will also only work if there is a valid transient record

to save. Otherwise it will report an error. A standard file save dialog box will appear with the

file type selectable as binary or text in the Save As Type selection box of the dialog.

The text data file format will contain a line of text for each sample. The samples are in

chronological order from oldest to newest. The resulting file will be quite large and will

probably need to be reduced for use in most data analysis programs. Some users may also find

it easier to understand this format than the binary format for use in custom post processing

software. Each line of the text file is formatted as follows.

Where: <Segment> is the memory segment in the range 0 to 31 dependant

on the current memory geometry settings

<Post Trigger> is 0 if the sample was taken before the trigger event

and 1 if the sample was taken after the trigger event

<Channel x> is the absolute value of the sample over the current full

scale range as an offset binary value of 0 to 4096 – that is, with the zero

volt level of input signal plus offset being 2048. This value includes any

effect of the instrument offset settings.

The binary file format contains sequential samples in a six byte equivalent to the line of

text in the text file format. It is written as a data structure from the C programming language and

stored with no padding between samples. Post processing software will need to be aware of this

structure’s format and will generally read data from the file into an equivalent structure to

preserve the byte ordering. The structure is as shown below, assuming the Windows software

conventions that a BYTE is an unsigned 8-bit number and a WORD is an unsigned 16-bit

number. The descriptions of the elements are equivalent to corresponding items in the text

format above.

typedef struct binary_data_record_st

{

BYTE segment;

BYTE trigger_valid;

WORD sample_ch1;

WORD sample_ch2;

} T_BINARY_DATA_RECORD;

Note that these data file formats do not contain any information about the settings of the

instrument from which they were written. Some information about the sample memory

geometry may be inferred, but other potentially important settings information must be recorded

separately if needed. The objective of the Save Data function is to save raw data for post

processing in its simplest possible format. Many post processing programs will require no more

data than this, while still others may require little else. Most will require a knowledge of the

sample rate or other basic points that the user might consider recording in the file name. All will

be affected in complexity and processing time by the size of the data file and anything other than

uniformity in its content. This is the logic behind the simple format given.

3.0 TR122 Software Source Code

Instruments such as the TR122 are only as useful as the software which runs them.

While the software provided with the TR122 makes the instrument very functional in a wide

variety of applications, it is impossible to predict the full range of possible user needs or the

software environment in which the instrument may be installed. Data Design has decided that

the best way to meet as many user needs as possible is to provide a window into the workings of

the instrument. To accomplish this, the source code for the software is published with the

software distribution.

This open source approach provides the user with nearly infinite flexibility. It also

provides the opportunity for many bad headaches. The inner workings of the software are not

for the novice user. Complex tricks and traps exist at every corner with an advanced instrument

such as the TR122. Concepts of multistage pipelines, direct memory address, advanced data

structures, threads, and other complexities must be understood. It is a challenge even for the

most skilled programmer. The good news is that the design is carefully structured and this

section of the manual provides a roadmap to the advanced user.

IMPORTANT NOTICE Information on source code and the source code itself is provided

AS IS and without warranty or support. Data Design is not able to provide technical

assistance to those attempting to modify the source code. It simply would not be possible to

provide the instrument at reasonable cost if such support were included in the price.

Please review the source code license agreement at the end of this manual before using the

source code. That said, however, Data Design does offer design services for hire. Information

can be found on the website at the front of this manual. Also, from time to time, additional

applications and source code will be posted on the website for free download.

It should be noted that this section of the manual covers the workings of a particular code

base for a particular instrument. Any such software works with a hardware-software interface

defined in part by the hardware itself. At the simplest level this interface amounts to writing

various command and configuration registers and reading various data and status registers. Still,

understanding many of the complexities found internal to the code base might require a working

knowledge of the hardware. The hardware itself is not discussed in this manual and is

considered somewhat proprietary to Data Design. While it will become evident in this

discussion that the hardware could also be modified to meet additional unique and complex

requirements, this is substantially beyond the scope of most users’ needs and abilities. As such,

to maximize the usability of the open source environment, the interface to hardware is left

somewhat abstract in order to simplify the discussion. This understanding should be kept in

mind when reviewing the source code and deciding what should or should not be modified.

While there is some discussion of hardware details within the source code itself, the

discussion in this manual is aimed at common reasons why an advanced user would require

access to the source code. These include such tasks as interfacing to a custom top level

application, connecting the instrument to an existing software environment, or using the

instrument in another operating system. As such, the discussion of the top level application

presented in section 2 is also limited, though the source code for that application is also provided.

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