Measurement Computing PCI-2511 User manual

PCI-2511
16-Bit, 1 MS/s Analog Input Board
User's Guide
January 2019. Rev 10
© Measurement Computing Corporation

2
PCI-2511
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Other product and company names mentioned herein are trademarks or trade names of their respective
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photocopying, recording, or otherwise without the prior written permission of Measurement Computing
Corporation.
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 that, 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.

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Table of Contents
Preface
About this User's Guide .......................................................................................................................5
What you will learn from this user's guide .........................................................................................................5
Conventions in this user's guide .........................................................................................................................5
Where to find more information .........................................................................................................................5
Chapter 1
Introducing the PCI-2511......................................................................................................................6
Overview: PCI-2511 features .............................................................................................................................6
Chapter 2
Installing the PCI-2511..........................................................................................................................7
Unpacking...........................................................................................................................................................7
Installing the software ........................................................................................................................................7
Installing the PCI-2511.......................................................................................................................................7
Configuring the hardware ...................................................................................................................................8
Signal connections..............................................................................................................................................8
Connector pinout............................................................................................................................................................... 8
Cabling ...............................................................................................................................................................9
Field wiring and signal termination .................................................................................................................................. 9
Installing multiple boards ...................................................................................................................................9
Chapter 3
Functional Details ...............................................................................................................................10
PCI-2511 block diagram...................................................................................................................................10
Synchronous I/O – mixing analog, digital, and counter scanning ....................................................................10
Bus mastering DMA.........................................................................................................................................11
Analog input .....................................................................................................................................................11
Analog input scanning .....................................................................................................................................................11
Digital I/O.........................................................................................................................................................12
Digital input scanning ......................................................................................................................................................12
Digital outputs and pattern generation .............................................................................................................................12
Triggering .........................................................................................................................................................12
Hardware analog triggering .............................................................................................................................................12
Digital triggering..............................................................................................................................................................13
Software-based triggering ................................................................................................................................................13
Stop trigger modes ...........................................................................................................................................................13
Pre-triggering and post-triggering modes ........................................................................................................................13
Counter inputs ..................................................................................................................................................14
Mapped channels .............................................................................................................................................................14
Counter modes .................................................................................................................................................................14
Debounce modes..............................................................................................................................................................15
Encoder mode ..................................................................................................................................................................18
Timer outputs....................................................................................................................................................21
Example: Timer outputs...................................................................................................................................................21
Using detection setpoints for output control.....................................................................................................22
What are detection setpoints? ..........................................................................................................................................22
Setpoint configuration overview......................................................................................................................................22
Setpoint configuration......................................................................................................................................................24
Using the setpoint status register......................................................................................................................................24
Examples of control outputs ............................................................................................................................................25
Detection setpoint details.................................................................................................................................................27
FIRSTPORTC or timer update latency ............................................................................................................................27

PCI-2511 User's Guide
4
Chapter 4
Calibrating the PCI-2511.....................................................................................................................29
Chapter 5
Specifications......................................................................................................................................30
Analog input .....................................................................................................................................................30
Accuracy..........................................................................................................................................................................30
Digital input / output.........................................................................................................................................31
Counters............................................................................................................................................................31
Input sequencer.................................................................................................................................................32
Frequency/pulse generators ..............................................................................................................................32
Trigger sources and modes ...............................................................................................................................33
Power consumption ..........................................................................................................................................33
PCI compatibility..............................................................................................................................................33
Environmental ..................................................................................................................................................34
Mechanical .......................................................................................................................................................34
Main connector and pinout ...............................................................................................................................34
Declaration of Conformity ..................................................................................................................36

5
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 PCI-2511 so that you get the most out of its
analog input, digital I/O, and counter/timer I/O features.
This user's guide also refers you to related documents available on our web site and to technical support
resources.
Conventions in this user's guide
For more information
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.
bold text Bold text is used for the names of objects on the screen, such as buttons, text boxes, and check boxes.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.
Where to find more information
Additional information about PCI-2511 hardware is available on our website at www.mccdaq.com. You can
also contact Measurement Computing Corporation with specific questions.
Knowledgebase: kb.mccdaq.com
Tech support form: www.mccdaq.com/support/support_form.aspx
Email: [e-mail]
Phone: [phone] and follow the instructions for reaching Tech Support
For international customers, contact your local distributor. Refer to the International Distributors section on our
web site at www.mccdaq.com/International.

6
Chapter 1
Introducing the PCI-2511
Overview: PCI-2511 features
The PCI-2511 board is a multifunction measurement and control board that is supported under popular
Microsoft®Windows®operating systems.
The PCI-2511 provides the following features:
16 single-ended analog inputs with 16-bit resolution and ±10 V input range
24 high-speed digital I/O lines
oUp to 4 MHz scanning on all digital input lines1.
Two timer outputs
Four 32-bit counters
Synchronous analog input, digital I/O, and counter/timer I/O operations
1Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.

7
Chapter 2
Installing the PCI-2511
Unpacking
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the device 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.
Contact us immediately if any components are missing or damaged.
Installing the software
Refer to the MCC DAQ Quick Start and the PCI-2511 product page on our website for information about the
software that supports the device.
Install the software before you install your device
The driver needed to run the PCI-2511 is installed with the software. Therefore, you need to install the software
package you plan to use before you install the hardware.
Installing the PCI-2511
The PCI-2511 board is completely plug-and-play. There are no switches or jumpers to set on the board.
Configuration is controlled by your system's BIOS.
Before you install the PCI-2511
Enable Bus Mastering DMA: For a PCI-2511 to operate properly, you must enable Bus Mastering DMA on the
PCI slot where you will install the board. Make sure that your computer can perform Bus Mastering DMA for
the applicable PCI slot. Some computers have BIOS settings that enable and disable Bus Mastering DMA. If
your computer has this BIOS option, make sure you enable Bus Mastering DMA on the appropriate PCI slot.
Refer to your PC Owner's Manual for additional information regarding your PC and enabling Bus Mastering
DMA for PCI slots.
Install the MCC DAQ software: The driver needed to run your PCI-2511 is installed with the MCC DAQ
software. Therefore, you need to install the MCC DAQ software before you install your board. Refer to the
MCC DAQ Quick Start for instructions on installing the software.
Perform the following procedure to install the PCI-2511:
1. Turn the computer off, open it up, and insert the board into an available PCI slot that has Bus Mastering
DMA enabled.
2. Close the computer and turn it on.
When connected for the first time, a Found New Hardware dialog opens when the operating system detects
the device. When the dialog closes, the installation is complete. If you have not installed the MCC DAQ
software, cancel the dialog and install it now.
3. To test the installation and configure your board, run the InstaCal utility installed in the previous section.
Refer to the MCC DAQ Quick Start for information on how to initially set up and load InstaCal.
If the board has been powered-off for more than 10 minutes, allow the computer to warm up for at least
30 minutes before acquiring data. This warm-up period is required in order for the board to achieve its rated
accuracy. The high speed components used on the board generate heat, and it takes this amount of time for a
board to reach steady state if it has been powered off for a significant amount of time.

PCI-2511 User's Guide Installing the PCI-2511
8
Configuring the hardware
All hardware configuration options on the PCI-2511 are software-controlled. You can select some of the
configuration options using InstaCal, such as the edge used for pacing when using an external clock. Once
selected, any program that uses the Universal Library initializes the hardware according to these selections.
For more information on signal connections
For general information regarding signal connection and configuration, refer to the Guide to Signal Connections
(available on our website at www.mccdaq.com/support/DAQ-Signal-Connections.aspx).
Signal connections
The table below lists board connectors, applicable cables, and compatible accessory products for the
PCI-2511.
Board connectors, cables, and compatible hardware
Connector type

68-pin standard "SCSI TYPE III" female connector

HDMI connector (targeted for future expansion)
Compatible cables (for the 68-pin
SCSI connector)
CA-68-3R — 68-pin ribbon cable; 3 feet.
CA-68-3S — 68-pin shielded round cable; 3 feet.
CA-68-6S — 68-pin shielded round cable; 6 feet.
Compatible accessory products TB-100 terminal connector
RM-TB-100
Connector pinout
16-channel single-ended mode pinout
Signal name Pin Pin Signal name
ACH0
68
••
34
ACH8
AGND
67
••
33
ACH1
ACH9
66
••
32
AGND
ACH2
65
••
31
ACH10
AGND
64
••
30
ACH3
ACH11)
63
••
29
AGND
SGND
62
••
28
ACH4
ACH12
61
••
27
AGND
ACH5
60
••
26
ACH13
AGND
59
••
25
ACH6
ACH14
58
••
24
AGND
ACH7
57
••
23
ACH15
NC
56
••
22
N/C
NC
55
••
21
N/C
NEGREF (reserved for self-calibration)
54
••
20
POSREF (reserved for self-calibration)
GND
53
••
19
+5V
A1
52
••
18
A0
A3
51
••
17
A2
A5
50
••
16
A4
A7
49
••
15
A6
B1
48
••
14
B0
B3
47
••
13
B2
B5
46
••
12
B4
B7
45
••
11
B6
C1
44
••
10
C0
C3
43
••
9
C2
C5
42
••
8
C4
C7
41
••
7
C6
GND
40
••
6
TTL TRG
CNT1
39
••
5
CNT0
CNT3
38
••
4
CNT2
TMR1
37
••
3
TMR0
GND
36
••
2
XAPCR
GND
35
••
1
XDPCR
PCI slot ↓

PCI-2511 User's Guide Installing the PCI-2511
9
Cabling
Use a CA-68-3R 68-pin ribbon expansion cable (Figure 1), or a CA-68-3S (3-foot) or CA-68-6S (6-foot) 68-pin
shielded expansion cable (Figure 2) to connect signals to the PCI-2511 board.)
Figure 1. CA-68-3R cable
Figure 2. CA-68-3S and CA-68-6S cable
Field wiring and signal termination
You can use the following MCC screw terminal boards to terminate field signals and route them into the
PCI-2511 board using the CA-68-3R, CA-68-3S, or CA-68-6S cable:
TB-100: Termination board with screw terminals.
RM-TB-100: 19-inch rack mount kit for the TB-100 termination board.
Details on these products are available on our website.
Installing multiple boards
PCI-2511 features can be replicated up to four times, as up to four boards can be installed in a single host PC.
The serial number on each PCI-2511 distinguishes one from another. You can operate multiple PCI-2511
boards synchronously. To do this, set up one PCI-2511 with the pacer pin you want to use (XAPCR or XDPCR)
configured for output. Set up the PCI-2511 boards you want to synchronize to this board with the pacer pin you
want to use (XAPCR or XDPCR) configured for input. Wire the pacer pin configured for output to each of the
pacer input pins that you want to synchronize.
The stripe
identifies pin # 1
6834
351
68
35
34
1
68
34
135
34
1
68
35

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Chapter 3
Functional Details
This chapter contains detailed information on all of the features available from the board, including:
a block diagram of board functions
information on how to use the signals generated by the board
diagrams of signals using default or conventional board settings
PCI-2511 block diagram
Figure 3is a simplified block diagram of the PCI-2511. This board provides all of the functional elements
shown in the figure.
Figure 3. PCI-2511 functional block diagram
Synchronous I/O – mixing analog, digital, and counter scanning
The PCI-2511 can read analog, digital, and counter inputs, while generating digital pattern outputs at the same
time. Digital and counter inputs do not affect the overall A/D rate because these inputs use no time slot in the
scanning sequencer.
For example, one analog input channel can be scanned at the full 1 MHz A/D rate along with digital and counter
input channels. Each analog channel can have a different gain, and counter and digital channels do not need
additional scanning bandwidth as long as there is at least one analog channel in the scan group.
Digital input channel sampling is not done during the "dead time" of the scan period where no analog sampling
is being done either.
The ability to scan digital and counter channels along with analog channels provides for a more deterministic
collection of data.

PCI-2511 User's Guide Functional Details
11
Bus mastering DMA
The PCI-2511 supports bus mastering DMA. With multiple DMA channels, analog, digital, and counter input
data, as well as digital output data, can flow between the PC and the PCI-2511 without consuming valuable
CPU time. The driver supplied with the PCI-2511 automatically uses bus mastering DMA to efficiently conduct
I/O from the PC to the PCI-2511.
Analog input
The PCI-2511 has a 16-bit, 1-MHz A/D coupled with 16 analog inputs. The input range is ±10 V.
Analog input scanning
The PCI-2511 has several scanning modes to address various applications. You can load the 512-location scan
buffer with any combination of analog input channels. All analog input channels in the scan buffer are measured
sequentially at 1 µs per channel by default.
For example, in the fastest mode, with 1 µs settling time for the acquisition of each channel, a single analog
channel can be scanned continuously at 1 MS/s; two analog channels can be scanned at 500 kS/s each; 16
analog input channels can be scanned at 62.5 kS/s.
Settling time
For most applications, leave the settling time at its default of 1 µs.
However, if you are scanning multiple channels, and one or more channels are connected to a high-impedance
source, you may get better results by increasing the settling time. Remember that increasing the settling reduces
the maximum acquisition rate.
You can set the settling time to 1 µs, 5 µs, 10 µs, or 1 ms.
Example: Analog channel scanning of voltage inputs
Figure 4shows a simple acquisition. The scan is programmed pre-acquisition and is made up of six analog
channels (Ch0, Ch1, Ch3, Ch4, Ch6, Ch7). Each of these analog channels can have a different gain. The
acquisition is triggered and the samples stream to the PC via DMA. Using the default settling time, each analog
channel requires one microsecond of scan time—therefore the scan period can be no shorter than 6 µs for this
example. The scan period can be made much longer than 6 µs—up to 1 second. The maximum scan frequency
is 1 divided by 6 µs, or 166,666 Hz.
Figure 4. Analog channel scan of voltage inputs example

PCI-2511 User's Guide Functional Details
12
Digital I/O
Twenty-four TTL-level digital I/O lines are included in each PCI-2511. You program digital I/O in 8-bit groups
as either inputs or outputs and can scan them in several modes (refer to "Digital input scanning" below). You
can access input ports asynchronously from the PC at any time, including when a scanned acquisition is
occurring.
Digital input scanning
Digital input ports can be read asynchronously before, during, or after an analog input scan.
Digital input ports can be part of the scan group and scanned along with analog input channels. Two
synchronous modes are supported when digital inputs are scanned along with analog inputs. In both modes,
adding digital input scans has no effect on the analog scan rate limitations. If no analog inputs are being
scanned, the digital inputs can sustain rates up to 4 MHz. Higher rates—up to 12 MHz—are possible depending
on the platform and the amount of data being transferred.
Digital outputs and pattern generation
Digital outputs can be updated asynchronously any time before, during, or after an acquisition. You can use two
of the 8-bit ports to generate a digital pattern at up to 4 MHz. The PCI-2511 supports digital pattern generation
with bus mastering DMA. The digital pattern can be read from PC RAM.
Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.
Digital pattern generation is clocked using an internal clock. The on-board programmable clock generates
updates ranging from once every 1 second to 1 MHz, independent of any acquisition rate.
Triggering
Triggering can be the most critical aspect of a data acquisition application. The PCI-2511 supports the
following trigger modes to accommodate certain measurement situations.
Hardware analog triggering
The PCI-2511 uses true analog triggering in which the trigger level you program sets an analog DAC, which is
then compared in hardware to the analog input level on the selected channel. This guarantees an analog trigger
latency that is less than 1 µs.
You can select any analog channel as the trigger channel, but the selected channel must be the first channel in
the scan. You can program the trigger level, the rising or falling edge, and hysteresis.
Hardware analog level trigger and the comparator change state
When analog input voltage starts near the trigger level, and you are performing a rising or falling hardware
analog level trigger, the analog level comparator may have already tripped before the sweep was enabled. If this
is the case, the circuit waits for the comparator to change state. However, since the comparator has already
changed state, the circuit does not see the transition.
Perform the following procedure to resolve this issue:
1. Set the analog level trigger to the threshold you want.
2. Apply an analog input signal that is more than 2.5% of the full-scale range away from the desired
threshold. This ensures that the comparator is in the proper state at the beginning of the acquisition.
3. Bring the analog input signal toward the desired threshold. When the input signal is at the threshold
(± some tolerance) the sweep will be triggered.
4. Before re-arming the trigger, move the analog input signal to a level that is more than 2.5% of the full-scale
range away from the desired threshold.
For example, if you are using the ±2 V full-scale range (gain = 5), and you want to trigger at +1 V on the rising
edge, you would set the analog input voltage to a start value that is less than +0.9 V (1 V – (2 V * 2 * 2.5%)).

PCI-2511 User's Guide Functional Details
13
Digital triggering
A separate digital trigger input line is provided (TTL TRG), allowing TTL-level triggering with latencies
guaranteed to be less than 1 µs. You can program both of the logic levels (1 or 0) and the rising or falling edge
for the discrete digital trigger input.
Software-based triggering
The three software-based trigger modes differ from hardware analog triggering and digital triggering because
the readings—analog, digital, or counter—are checked by the PC in order to detect the trigger event.
Analog triggering
You can select any analog channel in the scan as the trigger channel. You can program the trigger level, the
rising or falling edge, and hysteresis.
Pattern triggering
You can select any scanned digital input channel pattern to trigger an acquisition, including the ability to mask
or ignore specific bits.
Counter triggering
You can program triggering to occur when one of the counters meets or exceeds a set value, or is within a range
of values. You can program any of the included counter channels as the trigger source.
Software-based triggering usually results in a long period of inactivity between the trigger condition being
detected and the data being acquired. However, the PCI-2511 avoids this situation by using pre-trigger data.
When software-based-triggering is used, and the PC detects the trigger condition—which may be thousands of
readings after the actual occurrence of the signal—the PCI-2511 driver automatically looks back to the location
in memory where the actual trigger-causing measurement occurred, and presents the acquired data that begins at
the point where the trigger-causing measurement occurs. The maximum inactive period in this mode equals one
scan period.
Set pre-trigger > 0 when using a counter as the trigger source
When using a counter for a trigger source, you should use a pre-trigger with a value of at least 1. Since all
counters start at zero with the first scan, there is no valid reference in regard to rising or falling edge. Setting a
pre-trigger to 1 or more ensures that a valid reference value is present, and that the first trigger will be
legitimate.
Stop trigger modes
You can use any of the software trigger modes explained previously to stop an acquisition. For example, you
can program an acquisition to begin on one event, such as a voltage level, and then stop on another event, such
as a digital pattern.
Pre-triggering and post-triggering modes
The PCI-2511 supports four modes of pre-triggering and post-triggering, providing a wide-variety of options to
accommodate any measurement requirement. When using pre-trigger, you must use software-based triggering
to initiate an acquisition.
No pre-trigger, post-trigger stop event
Data acquisition starts when the trigger is received, and the acquisition stops when the stop-trigger event is
received.
Fixed pre-trigger with post-trigger stop event
You set the number of pre-trigger readings to acquire. The acquisition continues until a stop-trigger event
occurs.

PCI-2511 User's Guide Functional Details
14
No pre-trigger, infinite post-trigger
No pre-trigger data is acquired. Instead, data is acquired beginning with the trigger event, and is terminated
when you issue a command to halt the acquisition.
Fixed pre-trigger with infinite post-trigger
You set the amount of pre-trigger data to acquire. The system continues to acquire data until the program issues
a command to halt the acquisition.
Counter inputs
Four 32-bit counters are built into the PCI-2511. Each counter accepts frequency inputs up to 20 MHz. The
counter channels can be configured as standard counters or as multi-axis quadrature encoders.
The counters can concurrently monitor time periods, frequencies, pulses, and other event driven incremental
occurrences directly from pulse-generators, limit switches, proximity switches, and magnetic pick-ups.
Counter inputs can be read asynchronously under program control, or synchronously as part of an analog or
digital scan group.
When reading synchronously, all counters are set to zero at the start of an acquisition. When reading
asynchronously, counters may be cleared on each read, count up continually, or count until the 16 bit or 32 bit
limit has been reached. See counter mode descriptions below.
Figure 5. Typical PCI-2511 counter channel
Mapped channels
A mapped channel is one of four counter input signals that can get multiplexed into a counter module. The
mapped channel can participate with the counter's input signal by gating the counter, latching the counter, and
so on. The four possible choices for the mapped channel are the four counter input signals (post-debounce).
A mapped channel can be used to:
gate the counter
decrement the counter
latch to current count to the count register
Usually, all counter outputs are latched at the beginning of each scan within the acquisition. However, you can
use a second channel—known as the mapped channel— to latch the counter output.
Counter modes
A counter can be asynchronously read with or without clear on read. The asynchronous read-signals strobe
when the lower 16-bits of the counter are read by software. The software can read the counter's high 16-bits
some time later after reading the lower 16-bits. The full 32-bit result reflects the timing of the first
asynchronous read strobe.
Totalize mode
The Totalize mode allows basic use of a 32-bit counter. While in this mode, the channel's input can only
increment the counter upward. When used as a 16-bit counter (counter low), one channel can be scanned at the
12 MHz rate. When used as a 32-bit counter (counter high), two sample times are used to return the full 32-bit
result. Therefore a 32-bit counter can only be sampled at a 6 MHz maximum rate. If you only want the upper 16
bits of a 32-bit counter, then you can acquire that upper word at the 12 MHz rate.

PCI-2511 User's Guide Functional Details
15
The counter counts up and does not clear on every new sample. However, it does clear at the start of a new scan
command.
The counter rolls over on the 16-bit (counter low) boundary, or on the 32-bit (counter high) boundary.
Clear on read mode
The counter counts up and is cleared after each read. By default, the counter counts up and only clears the
counter at the start of a new scan command. The final value of the counter —the value just before it was
cleared—is latched and returned to the PCI-2511.
Stop at the top mode
The counter stops at the top of its count. The top of the count is FFFF hex (65,535) for the 16-bit mode, and
FFFFFFFF hex (4,294,967,295) for the 32-bit mode.
32-bit or 16-bit
Sets the counter type to either 16-bits or 32-bits. The type of counter only matters if the counter is using the stop
at the top mode—otherwise, this option is ignored.
Latch on map
Sets the signal on the mapped counter input to latch the count.
By default, the start of scan signal—a signal internal to the PCI-2511 pulses once every scan period to indicate
the start of a scan group—latches the count, so the count is updated each time a scan is started.
Gating "on" mode
Sets the gating option to "on" for the mapped channel, enabling the mapped channel to gate the counter.
Any counter can be gated by the mapped channel. When the mapped channel is high, the counter is enabled.
When the mapped channel is low, the counter is disabled (but holds the count value). The mapped channel can
be any counter input channel other than the counter being gated.
Decrement "on" mode
Sets the counter decrement option to "on" for the mapped channel. The input channel for the counter increments
the counter, and you can use the mapped channel to decrement the counter.
Debounce modes
Each channel's output can be debounced with 16 programmable debounce times from 500 ns to 25.5 ms. The
debounce circuitry eliminates switch-induced transients typically associated with electro-mechanical devices
including relays, proximity switches, and encoders.
There are two debounce modes, as well as a debounce bypass, as shown in Figure 6. In addition, the signal from
the buffer can be inverted before it enters the debounce circuitry. The inverter is used to make the input rising-
edge or falling-edge sensitive.
Edge selection is available with or without debounce. In this case the debounce time setting is ignored and the
input signal goes straight from the inverter or inverter bypass to the counter module.
There are 16 different debounce times. In either debounce mode, the debounce time selected determines how
fast the signal can change and still be recognized.
The two debounce modes are trigger after stable and trigger before stable. A discussion of the two modes
follows.

PCI-2511 User's Guide Functional Details
16
Figure 6. Debounce model block diagram
Trigger after stable mode
In the trigger after stable mode, the output of the debounce module does not change state until a period of
stability has been achieved. This means that the input has an edge, and then must be stable for a period of time
equal to the debounce time.
Figure 7. Debounce module – trigger after stable mode
The following time periods (T1 through T5) pertain to Figure 7. In trigger after stable mode, the input signal to
the debounce module is required to have a period of stability after an incoming edge, in order for that edge to be
accepted (passed through to the counter module.) The debounce time for this example is equal to T2 and T5.
T1 – In the example above, the input signal goes high at the beginning of time period T1, but never stays
high for a period of time equal to the debounce time setting (equal to T2 for this example.)
T2 – At the end of time period T2, the input signal has transitioned high and stayed there for the required
amount of time—therefore the output transitions high. If the input signal does not stabilize in the high state
long enough, no transition would have appeared on the output and the entire disturbance on the input would
have been rejected.
T3 – During time period T3, the input signal remained steady. No change in output is seen.
T4 – During time period T4, the input signal has more disturbances and does not stabilize in any state long
enough. No change in the output is seen.
T5 – At the end of time period T5, the input signal has transitioned low and stayed there for the required
amount of time—therefore the output goes low.
Trigger before stable mode
In the trigger before stable mode, the output of the debounce module immediately changes state, but will not
change state again until a period of stability has passed. For this reason the mode can be used to detect glitches.
Figure 8. Debounce module – Trigger before stable mode
The following time periods (T1 through T6) pertain to the above drawing.

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T1 – In the illustrated example, the input signal is low for the debounce time (equal to T1); therefore when
the input edge arrives at the end of time period T1, it is accepted and the output (of the debounce module)
goes high. Note that a period of stability must precede the edge in order for the edge to be accepted.
T2 – During time period T2, the input signal is not stable for a length of time equal to T1 (the debounce
time setting for this example.) Therefore, the output stays "high" and does not change state during time
period T2.
T3 – During time period T3, the input signal is stable for a time period equal to T1, meeting the debounce
requirement. The output is held at the high state. This is the same state as the input.
T4 – At anytime during time period T4, the input can change state. When this happens, the output will also
change state. At the end of time period T4, the input changes state, going low, and the output follows this
action [by going low].
T5 – During time period T5, the input signal again has disturbances that cause the input to not meet the
debounce time requirement. The output does not change state.
T6 – After time period T6, the input signal has been stable for the debounce time and therefore any edge on
the input after time period T6 is immediately reflected in the output of the debounce module.
Debounce mode comparisons
Figure 9 shows how the two modes interpret the same input signal, which exhibits glitches. Notice that the
trigger before stable mode recognizes more glitches than the trigger after stable mode. Use the bypass option to
achieve maximum glitch recognition.
Figure 9. Example of two debounce modes interpreting the same signal
Debounce times should be set according to the amount of instability expected in the input signal. Setting a
debounce time that is too short may result in unwanted glitches clocking the counter. Setting a debounce time
too long may result in an input signal being rejected entirely. Some experimentation may be required to find the
appropriate debounce time for a particular application.
To see the effects of different debounce time settings, simply view the analog waveform along with the counter
output. This can be done by connecting the source to an analog input.
Use trigger before stable mode when the input signal has groups of glitches and each group is to be counted as
one. The trigger before stable mode recognizes and counts the first glitch within a group but rejects the
subsequent glitches within the group if the debounce time is set accordingly. The debounce time should be set
to encompass one entire group of glitches as shown in the following diagram.
Figure 10.Optimal debounce time for trigger before stable mode

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Trigger after stable mode behaves more like a traditional debounce function: rejecting glitches and only passing
state transitions after a required period of stability. Trigger after stable mode is used with electro-mechanical
devices like encoders and mechanical switches to reject switch bounce and disturbances due to a vibrating
encoder that is not otherwise moving. The debounce time should be set short enough to accept the desired input
pulse but longer than the period of the undesired disturbance as shown in Figure 11.
Figure 11. Optimal debounce time for trigger after stable mode
Encoder mode
Rotary shaft encoders are frequently used with CNC equipment, metal-working machines, packaging
equipment, elevators, valve control systems, and in a multitude of other applications in which rotary shafts are
involved.
The encoder mode allows the PCI-2511 to use data from optical incremental quadrature encoders. In encoder
mode, the PCI-2511 accepts single-ended inputs. When reading phase A, phase B, and index Z signals, the PCI-
2511 provides positioning, direction, and velocity data.
The PCI-2511 can receive input from up to two encoders.
The PCI-2511 supports quadrature encoders with a 16-bit (counter low) or a 32-bit (counter high) counter,
20 MHz frequency, and X1, X2, and X4 count modes. With only phase A and phase B signals, two channels are
supported; with phase A, phase B, and index Z signals, 1 channel is supported. Each input can be debounced
from 500 ns to 25.5 ms (total of 16 selections) to eliminate extraneous noise or switch induced transients.
Encoder input signals must be within -5 V to +10 V and the switching threshold is TTL (1.3V).
Quadrature encoders generally have three outputs: A, B, and Z. The A and B signals are pulse trains driven by
an optical sensor inside the encoder. As the encoder shaft rotates, a laminated optical shield rotates inside the
encoder. The shield has three concentric circular patterns of alternating opaque and transparent windows
through which an LED shines. There is one LED and one phototransistor for each of the concentric circular
patterns. One phototransistor produces the A signal, another phototransistor produces the B signal and the last
phototransistor produces the Z signal. The concentric pattern for A has 512 window pairs (or 1024, 4096, etc.)
When using a counter for a trigger source, use a pre-trigger with a value of at least 1. Since all counters start at
zero with the initial scan, there is no valid reference in regard to rising or falling edge. Setting a pre-trigger to
1 or more ensures that a valid reference value is present and that the first trigger is legitimate.

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The concentric pattern for B has the same number of window pairs as A—except that the entire pattern is
rotated by 1/4 of a window-pair. Thus the B signal is always 90° out of phase from the A signal. The A and B
signals pulse 512 times (or 1024, 4096, etc.) per complete rotation of the encoder.
The concentric pattern for the Z signal has only one transparent window and therefore pulses only once per
complete rotation. Representative signals are shown in the following figure.
Figure 12. Representation of quadrature encoder outputs: A, B, and Z
As the encoder rotates, the A (or B) signal indicates the distance the encoder has traveled. The frequency of A
(or B) indicates the velocity of rotation of the encoder. If the Z signal is used to zero a counter (that is clocked
by A) then that counter gives the number of pulses the encoder has rotated from its reference. The Z signal is a
reference marker for the encoder. It should be noted that when the encoder is rotating clockwise (as viewed
from the back), A leads B and when the encoder is rotating counterclockwise, A lags behind B. If the counter
direction control logic is such that the counter counts upward when A leads B and counts downward when A
lags B, then the counter gives direction control as well as distance from the reference.
Maximizing encoder accuracy
If there are 512 pulses on A, the encoder position is accurate to within 360°/512.
For a position accuracy of 360°/1024, count both rising edges on A and falling edges on A.
You get maximum accuracy when counting rising and falling edges on A and on B (since B also has 512
pulses.) This gives a position accuracy of 360°/2048.
These different modes are known as X1, X2, and X4.
Connecting the PCI-2511 to an encoder
You can use up to two encoders with each PCI-2511 in your acquisition system. Each A and B signal can be
made as a single-ended connection with respect to common ground.
Differential applications are not supported.
For single-ended applications:
Connect signals A, B, and Z to the counter inputs on the PCI-2511.
Connect each encoder ground to GND.
You can also connect external pull-up resistors to the PCI-2511 counter input terminal blocks by placing a pull-
up resistor between any input channel and the encoder power supply. Choose a pull-up resistor value based on
the encoder's output drive capability and the input impedance of the PCI-2511. Lower values of pull-up resistors
cause less distortion, but also cause the encoder's output driver to pull down with more current.
Connecting external pull-up resistors to the PCI-2511
For open-collector outputs, you can connect external pull-up resistors to the PCI-2511's counter input terminal
blocks. You can place a pull-up resistor between any input channel and the provided +5 V power supply.
Choose a pull-up resistor value based on the encoder's output drive capability and the input impedance of the
PCI-2511. Lower values of pull-up resistors cause less distortion but also cause the encoder's output driver to
pull down with more current.
Wiring to one encoder: Figure 13 shows the connections for one encoder to a 68-pin SCSI connector on a PCI-
2511. The "A" signal must be connected to an even-numbered channel and the associated "B" signal must be
connected to the next [higher] odd-numbered channel. For example, if "A" were connected to CTR0, "B" would
be connected to CTR1.
A
B
Z

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Figure 13. Encoder connections to pins on the SCSI connector*
* Connections can instead be made to the associated screw-terminals of a connected TB-100 terminal connector
option.
The "A" signal must be connected to an even-numbered channel and the associated "B" signal must be
connected to the next higher odd-numbered channel. For example, if "A" were connected to counter 0, then "B"
would be connected to counter 1.
If the encoder stops rotating, but is vibrating (due to it being mounted to a machine), you can use the debounce
feature to eliminate false edges. Choose an appropriate debounce time and apply it to each encoder channel.
Refer to the Debounce modes section in the Functional Details chapter in this manual for additional information
regarding debounce times.
You can get the relative position and velocity from the encoder. However, during an acquisition, you cannot get
data that is relative to the Z-position until the encoder locates the Z-reference.
Note that the number of Z-reference crossings can be tabulated. If the encoder was turning in only one direction,
then the Z-reference crossings equal the number of complete revolutions. This means that the data streaming to
the PC is relative position, period = 1/velocity, and revolutions.
A typical acquisition is shown in Figure 14. You determine the scan rate and the number of scans to take.
Figure 14. PCI-2511 acquisition of six readings per scan
Note: Digital channels do not take up analog channel scan time.
In general, the output of each channel’s counter is latched at the beginning of each scan period (called the start-
of-scan.) Every time the PCI-2511 receives a start-of-scan signal, the counter values are latched and are
available to the PCI-2511.
The PCI-2511 clears all counter channels at the beginning of the acquisition. This means that the values
returned during scan period 1 are always zero. The values returned during scan period 2 reflect what happened
during scan period 1. The scan period defines the timing resolution for the PCI-2511. If you need a higher
timing resolution, shorten the scan period.
Wiring for two encoders: Figure 15 shows the single-ended connections for two encoders. Differential
connections do not apply.
Ground (to Digital Common pin 35, 36, 40)
Counter 0 (CNT0, pin 5) – To Encoder “A”
Counter 1 (CNT1, pin 39) – To Encoder “B”
Counter 2 (CNT2, pin 4) – To Encoder “Z”
+5 VDC, pin 19
To ground (of external power source)