PCI/PXI/USB-6255 Specifications

Specifications

These specifications apply to the PCI-6255, PXI-6255, USB-6255 Screw Terminal, USB-6255 Mass Termination, and USB-6255 OEM models.

The following specifications are typical at 25 °C, unless otherwise noted.

Revision History

Version	Date changed	Description
375215E-01	August 2025	Updated I/O connector specifications.
375215D-01	June 2025	Added pinout diagrams.
375215C-01	June 2016	Updated AI crosstalk specification and AI absolute accuracy example values.
375215B-01	September 2015	Updated formatting.
375215A-01	May 2015	Initial release.
371291H-01	June 2007	Original specifications document: NI 625x Specifications.

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PCI/PXI/USB-6255 Pinout

Use the pinout to connect to terminals on the PCI/PXI/USB-6255.

Figure 2. USB-6255 Screw Terminal Pinout

Figure 3. USB-6255 Mass Termination Pinout

Analog Input

Table 1. Analog Input Characteristics
Number of channels	40 differential or 80 single ended
ADC resolution	16 bits
DNL	No missing codes guaranteed
INL	Refer to AI Absolute Accuracy
Timing accuracy	50 ppm of sample rate
Timing resolution	50 ns
Input coupling	DC
Input range	±0.1 V, ±0.2 V, ±0.5 V, ±1 V, ±2 V, ±5 V, ±10 V
Maximum working voltage for analog inputs (signal + common mode)	±11 V of AI GND
CMRR (DC to 60 Hz)	100 dB
Input bias current	±100 pA
Small signal bandwidth (-3 dB)	1.7 MHz
Input FIFO size	4,095 samples
Scan list memory	4,095 entries

Table 2. AI Sample Rate
Single channel maximum	1.25 MS/s
Multichannel maximum (aggregate)	750 kS/s
Minimum	No minimum

Table 3. AI Input Impedance
Device on, AI+ to AI GND	>10 GΩ in parallel with 100 pF
Device on, AI- to AI GND	>10 GΩ in parallel with 100 pF
Device off, AI+ to AI GND	820 Ω
Device off, AI- to AI GND	820 Ω

Table 4. AI Crosstalk (at 100 kHz)
Adjacent channels	-75 dB
Non-adjacent channels	-95 dB. See note.

Note Channel AI <0..15> crosstalk to channel AI <64..79> is -67 dB. This applies to channels with 64-channel separation. Example: AI (x) and AI (x + 64).

Table 5. AI Data Transfers
PCI/PXI	DMA (scatter-gather), interrupts, programmed I/O
USB	USB Signal Stream, programmed I/O

Table 6. AI Overvoltage Protection for All Analog Input and Sense Channels
Device on	±25 V for up to four AI pins
Device off	±15 V for up to four AI pins

Table 7. AI Input Current During Overvoltage Condition
Input current during overvoltage condition	±20 mA maximum/AI pin

Settling Time for Multichannel Measurements

Table 8. Settling Time for Multichannel Measurements
Range	±60 ppm of Step (±4 LSB for Full-Scale Step)	±15 ppm of Step (±1 LSB for Full-Scale Step)
±1 V, ±2 V, ±5 V, ±10 V	1.3 μs	1.6 μs
±0.5 V	1.8 μs	2.5 μs
±0.1 V, ±0.2 V	3 μs	8 μs

Typical Performance Graphs

Figure 4. Settling Error versus Time for Different Source Impedances

AI Absolute Accuracy

Note Accuracies listed are valid for up to two years from the device external calibration.

Table 9. AI Absolute Accuracy
Nominal Range Positive Full Scale	Nominal Range Negative Full Scale	Residual Gain Error (ppm of Reading)	Residual Offset Error (ppm of Range)	Offset Tempco (ppm of Range/°C)	Random Noise, σ (μVrms)	Absolute Accuracy at Full Scale (μV)	Sensitivity (μV)
10	-10	60	20	21	280	1,920	112.0
5	-5	70	20	21	140	1,010	56.0
2	-2	70	20	24	57	410	22.8
1	-1	80	20	27	32	220	12.8
0.5	-0.5	90	40	34	21	130	8.4
0.2	-0.2	130	80	55	16	74	6.4
0.1	-0.1	150	150	90	15	52	6.0

Note Sensitivity is the smallest voltage change that can be detected. It is a function of noise.

Table 10. AI Absolute Accuracy Values
Gain tempco	13 ppm/°C
Reference tempco	1 ppm/°C
INL error	60 ppm of range

AI Absolute Accuracy Equation

AbsoluteAccuracy = Reading · (GainError) + Range · (OffsetError) + NoiseUncertainty

GainError = ResidualAIGainError + GainTempco · (TempChangeFromLastInternalCal) + ReferenceTempco · (TempChangeFromLastExternalCal)
OffsetError = ResidualAIOffsetError + OffsetTempco · (TempChangeFromLastInternalCal) + INLError
NoiseUncertainty =
$\frac{Random Noise \cdot 3}{\sqrt{100}}$
for a coverage factor of 3 σ and averaging 100 points.

AI Absolute Accuracy Example

Absolute accuracy at full scale on the analog input channels is determined using the following assumptions:

TempChangeFromLastExternalCal = 10 °C
TempChangeFromLastInternalCal = 1 °C
number_of_readings = 100
CoverageFactor = 3 σ

For example, on the 10 V range, the absolute accuracy at full scale is as follows:

GainError = 60 ppm + 13 ppm · 1 + 1 ppm · 10 = 83 ppm
OffsetError = 20 ppm + 21 ppm · 1 + 60 ppm = 101 ppm
NoiseUncertainty =
$\frac{280 µ V \cdot 3}{\sqrt{100}}$
= 84 µV
AbsoluteAccuracy = 10 V · (GainError) + 10 V · (OffsetError) + NoiseUncertainty = 1,920 µV

Analog Triggers

Table 11. Analog Triggers
Number of triggers	1
Source	AI <0..79>, API 0
Functions	Start Trigger, Reference Trigger, Pause Trigger, Sample Clock, Convert Clock, Sample Clock Timebase
Resolution	10 bits, 1 in 1,024
Modes	Analog edge triggering, analog edge triggering with hysteresis, and analog window triggering
Accuracy	±1%

Table 12. Analog Trigger Source Level
AI <0..79>	±Full scale
APFI 0	±10 V

Table 13. Analog Trigger Bandwidth (-3 dB)
AI <0..79>	3.4 MHz
APFI 0	3.9 MHz

Table 14. APFI 0 Characteristics
Input impedance	10 kΩ
Coupling	DC
Protection, power on	±30 V
Protection, power off	±15 V

Analog Output

Table 15. Analog Output Characteristics
Number of channels	2
DAC resolution	16 bits
DNL	±1 LSB
Monotonicity	16 bit guaranteed
Accuracy	Refer to AO Absolute Accuracy
Timing accuracy	50 ppm of sample rate
Timing resolution	50 ns
Output range	±5 V, ±10 V, ±external reference on APFI 0
Output coupling	DC
Output impedance	0.2 Ω
Output current drive	±5 mA
Overdrive protection	±25 V
Overdrive current	20 mA
Power-on state	±5 mV^[1]¹ When the USB Screw Terminal device is powered on, the analog output signal is not defined until after USB configuration is complete.
Power-off glitch	1.5 V peak for 1.5 s
Output FIFO size	8,191 samples shared among channels used
AO waveform modes	Non-periodic waveform, periodic waveform regeneration mode from onboard FIFO, periodic waveform regeneration from host buffer including dynamic update
Settling time, full-scale step, 15 ppm (1 LSB)	2 µs
Slew rate	20 V/µs

Table 16. AO Maximum Update Rate
1 channel	2.86 MS/s
2 channels	2.00 MS/s per channel

Table 17. AO Data Transfers
PCI/PXI	DMA (scatter-gather), interrupts, programmed I/O
USB	USB Signal Stream, programmed I/O

Table 18. AO Glitch Energy at Midscale Transition, ±10 V Range
Magnitude	10 mV
Duration	1 µs

External Reference

Table 19. APFI 0 Characteristics
Input impedance	10 kΩ
Coupling	DC
Protection, power on	±30 V
Protection, power off	±15 V
Range	± 11 V
Slew rate	20 V/μs

AO Absolute Accuracy

Absolute accuracy at full-scale numbers is valid immediately following internal calibration and assumes the device is operating within 10 °C of the last external calibration.

Note Accuracies listed are valid for up to two years from the device external calibration.

Table 20. AO Absolute Accuracy
Nominal Range Positive Full Scale	Nominal Range Negative Full Scale	Residual Gain Error (ppm of Reading)	Gain Tempco (ppm/°C)	Residual Offset Error (ppm of Range)	Offset Tempco (ppm of Range/°C)	Absolute Accuracy at Full Scale (μV)
10	-10	75	17	40	2	2,080
5	-5	85	8	40	2	1,045

Table 21. AO Absolute Accuracy Values
Reference tempco	1 ppm/°C
INL error	64 ppm of range

AO Absolute Accuracy Equation

AbsoluteAccuracy = OutputValue · (GainError) + Range · (OffsetError)

GainError = ResidualGainError + GainTempco · (TempChangeFromLastInternalCal) + ReferenceTempco · (TempChangeFromLastExternalCal)
OffsetError = ResidualOffsetError + AOOffsetTempco · (TempChangeFromLastInternalCal) + INLError

Digital I/O/PFI

Static Characteristics

Table 22. Static DIO/PFI Characteristics
Number of channels	24 total, 8 (P0.<0..7>), 16 (PFI <0..7>/P1, PFI <8..15>/P2)
Ground reference	D GND
Direction control	Each terminal individually programmable as input or output
Pull-down resistor	50 kΩ typical, 20 kΩ minimum
Input voltage protection	±20 V on up to two pins^[2]² Stresses beyond those listed under Input voltage protection may cause permanent damage to the device.

Waveform Characteristics (Port 0 Only)

Table 23. DIO Waveform Characteristics (Port 0 Only)
Terminals used	Port 0 (P0.<0..7>)
Port/sample size	Up to 8 bits
Waveform generation (DO) FIFO	2,047 samples
Waveform acquisition (DI) FIFO	2,047 samples
DI or DO Sample Clock source^[3]³ The digital subsystem does not have its own dedicated internal timing engine. Therefore, a sample clock must be provided from another subsystem on the device or an external source.	Any PFI, RTSI, AI Sample or Convert Clock, AO Sample Clock, Ctr n Internal Output, and many other signals

Table 24. DI Sample Clock Frequency
PCI/PXI	0 MHz to 10 MHz, system and bus activity dependent
USB	0 MHz to 1 MHz, system and bus activity dependent

Table 25. DO Sample Clock Frequency (PCI/PXI)
Regenerate from FIFO	0 MHz to 10 MHz
Streaming from memory	0 to 10 MHz, system and bus activity dependent

Table 26. DO Sample Clock Frequency (USB)
Regenerate from FIFO	0 MHz to 10 MHz
Streaming from memory	0 MHz to 1 MHz, system and bus activity dependent

Table 27. Data Transfers
PCI/PXI	DMA (scatter-gather), interrupts, programmed I/O
USB	USB Signal Stream, programmed I/O

PFI/Port 1/Port 2 Functionality

Table 28. PFI/Port 1/Port 2 Functionality
Functionality	Static digital input, static digital output, timing input, timing output
Timing output sources	Many AI, AO, counter, DI, DO timing signals
Debounce filter settings	125 ns, 6.425 µs, 2.56 ms, disable; high and low transitions; selectable per input

Recommended Operating Conditions


Level	Minimum	Maximum
Input high voltage (V_IH)	2.2 V	5.25 V
Input low voltage (V_IL)	0 V	0.8 V
Output high current (I_OH) P0.<0..7>	—	-24 mA
Output high current (I_OH) PFI <0..15>/P1/P2	—	-16 mA
Output low current (I_OL) P0.<0..7>	—	24 mA
Output low current (I_OL) PFI <0..15>/P1/P2	—	16 mA

Electrical Characteristics


Level	Minimum	Maximum
Positive-going threshold (VT+)	—	2.2 V
Negative-going threshold (VT-)	0.8 V	—
Delta VT hysteresis (VT+ - VT-)	0.2 V	—
I_IL input low current (V_in = 0 V)	—	-10 µA
I_IH input high current (V_in = 5 V)	—	250 µA

Digital I/O Characteristics

Figure 9. PFI <0..15>/P1/P2: I_oh versus V_oh

Figure 11. PFI <0..15>/P1/P2: I_ol versus V_ol

General-Purpose Counters/Timers

Table 29. General-Purpose Counters/Timer Characteristics
Number of counter/timers	2
Resolution	32 bits
Counter measurements	Edge counting, pulse, semi-period, period, two-edge separation
Position measurements	X1, X2, X4 quadrature encoding with Channel Z reloading; two-pulse encoding
Output applications	Pulse, pulse train with dynamic updates, frequency division, equivalent time sampling
Internal base clocks	80 MHz, 20 MHz, 0.1 MHz
External base clock frequency	0 MHz to 20 MHz
Base clock accuracy	50 ppm
Inputs	Gate, Source, HW_Arm, Aux, A, B, Z, Up_Down
Routing options for inputs	Any PFI, RTSI, PXI_TRIG, PXI_STAR, analog trigger, many internal signals
FIFO	2 samples

Table 30. Counter/Timer Data Transfers
PCI/PXI	Dedicated scatter-gather DMA controller for each counter/timer; interrupts, programmed I/O
USB	USB Signal Stream, programmed I/O

Frequency Generator

Table 31. Frequency Generator Characteristics
Number of channels	1
Base clocks	10 MHz, 100 kHz
Divisors	1 to 16
Base clock accuracy	50 ppm

Output can be available on any output PFI or RTSI terminal.

Phase-Locked Loop (PLL) (PCI/PXI Only)

Table 32. PLL Characteristics
Number of PLLs	1
Reference signal	PXI_STAR, PXI_CLK10, RTSI <0..7>
Output of PLL	80 MHz Timebase; other signals derived from 80 MHz Timebase including 20 MHz and 100 kHz Timebases

External Digital Triggers

Table 33. External Digital Triggers
Source	Any PFI, RTSI, PXI_TRIG, PXI_STAR
Polarity	Software-selectable for most signals
Analog input function	Start Trigger, Reference Trigger, Pause Trigger, Sample Clock, Convert Clock, Sample Clock Timebase
Analog output function	Start Trigger, Pause Trigger, Sample Clock, Sample Clock Timebase
Counter/timer function	Gate, Source, HW_Arm, Aux, A, B, Z, Up_Down
Digital waveform generation (DO) function	Sample Clock
Digital waveform acquisition (DI) function	Sample Clock

Device-to-Device Trigger Bus

Table 34. Device-to-Device Trigger Bus
PCI	RTSI <0..7>^[4]⁴ In other sections of this document, RTSI refers to RTSI <0..7> for the PCI devices or PXI_TRIG <0..7> for PXI devices.
PXI	PXI_TRIG <0..7>, PXI_STAR
USB source	None
Output selections	10 MHz Clock, frequency generator output, many internal signals
Debounce filter settings	125 ns, 6.425 μs, 2.56 ms, disable; high and low transitions; selectable per input

Bus Interface

Table 35. Bus Interface Characteristics
PCI/PXI	3.3 V or 5 V signal environment
USB	USB 2.0 Hi-Speed or full-speed^[5]⁵ If you are using an USB M Series device in full-speed mode, device performance will be lower and you will not be able to achieve maximum sample/update rates.^,^[6]⁶ Operating on a full-speed bus may result in lower performance.
DMA channels (PCI/PXI)	6, can be used for analog input, analog output, digital input, digital output, counter/timer 0, counter/timer 1
USB Signal Stream	4, can be used for analog input, analog output, counter/timer 0, counter/timer 1
The PXI module can be installed in PXI Express hybrid slots. It cannot be used to control SCXI in PXI/SCXI combo chassis.

Power Requirements

Table 36. PCI/PXI Current Draw from Bus During No-Load Condition (Does Not Include P0/PFI/P1/P2 and +5 V Terminals)
+5 V	0.03 A
+3.3 V	0.725 A
+12 V	0.35 A

Note Older revisions of the PCI/PXI device have a self-resetting fuse that opens when current exceeds the current limit on the +5 V terminal. Newer revisions of the device have a traditional fuse that opens when current exceeds this specification. This fuse is not customer-replaceable; if the fuse permanently opens, return the device to NI for repair.

Table 37. PCI/PXI Current Draw from Bus During AI and AO Overvoltage Condition (Does Not Include P0/PFI/P1/P2 and +5 V Terminals)
+5 V	0.03 A
+3.3 V	1.2 A
+12 V	0.38 A

Note Older revisions of the PCI/PXI device have a self-resetting fuse that opens when current exceeds the current limit on the +5 V terminal. Newer revisions of the device have a traditional fuse that opens when current exceeds this specification. This fuse is not customer-replaceable; if the fuse permanently opens, return the device to NI for repair.

Caution USB devices must be powered with an NI offered AC adapter or a National Electric Code (NEC) Class 2 DC source that meets the power requirements for the device and has appropriate safety certification marks for country of use.

Table 38. USB Power Supply Requirements
USB power supply requirements	11 VDC to 30 VDC, 20 W, locking or non-locking power jack with 0.080 in. diameter center pin, 5/16-32 thread for locking collars

Current Limits

Caution Exceeding the current limits may cause unpredictable behavior by the device and/or PC/chassis.

Table 39. PCI Current Limits
+5 V terminal (connector 0)	1 A maximum. See note.
+5 V terminal (connector 1)	1 A maximum. See note.

Note Older revisions of the PCI device have a self-resetting fuse that opens when current exceeds the current limit on the +5 V terminal. Newer revisions of the device have a traditional fuse that opens when current exceeds this specification. This fuse is not customer-replaceable; if the fuse permanently opens, return the device to NI for repair.

Table 40. PXI Current Limits
+5 V terminal (connector 0)	1 A maximum. See note.
+5 V terminal (connector 1)	1 A maximum. See note.
P0/PFI/P1/P2 and +5 V terminals combined	2 A maximum

Note Older revisions of the PXI module have a self-resetting fuse that opens when current exceeds the current limit on the +5 V terminal. Newer revisions of the module have a traditional fuse that opens when current exceeds this specification. This fuse is not customer-replaceable; if the fuse permanently opens, return the device to NI for repair.

Table 41. USB Current Limits
+5 V terminal	1 A maximum. See note.
P0/PFI/P1/P2 and +5 V terminals combined	2 A maximum
Power supply fuse	2 A, 250 V

Note Older revisions of the USB device have a self-resetting fuse that opens when current exceeds the current limit on the +5 V terminal. Newer revisions of the device have a traditional fuse that opens when current exceeds this specification. This fuse is not customer-replaceable; if the fuse permanently opens, return the device to NI for repair.

Physical Characteristics

Table 42. Dimensions
PCI printed circuit board	10.6 cm × 15.5 cm (4.2 in. × 6.1 in.)
PXI printed circuit board	Standard 3U PXI
USB Screw Terminal (includes connectors)	26.67 cm × 17.09 cm × 4.45 cm (10.5 in. × 6.73 in. × 1.75 in.)
USB Mass Termination (includes connectors)	18.8 cm × 17.09 cm × 4.45 cm (7.4 in. × 6.73 in. × 1.75 in.)
USB OEM	Refer to the NI USB-622x/625x/628x OEM User Guide

Table 43. Weight
PCI	164 g (5.8 oz)
PXI	236 g (8.3 oz)
USB Screw Terminal	1.24 kg (2 lb11 oz)
USB Mass Termination	816 g (1 lb12.8 oz)
USB OEM	172 g (6.1 oz)

Table 44. I/O Connectors
PCI/PXI	2 68-pin VHDCI
USB Screw Terminal	128 screw terminals
USB Mass Termination	2 68-pin SCSI

Table 45. Screw Terminal Wiring
USB screw terminal wiring	16 AWG to 28 AWG

Calibration

Table 46. Calibration
PCI/PXI recommended warm-up time	15 minutes
USB recommended warm-up time	30 minutes
Calibration interval	2 years

Maximum Working Voltage

Connect only voltages that are below these limits.

Table 47. Maximum Working Voltage
Channel-to-earth	11 V, Measurement Category I

Measurement Category I is for measurements performed on circuits not directly connected to the electrical distribution system referred to as MAINS voltage. MAINS is a hazardous live electrical supply system that powers equipment. This category is for measurements of voltages from specially protected secondary circuits. Such voltage measurements include signal levels, special equipment, limited-energy parts of equipment, circuits powered by regulated low-voltage sources, and electronics.

Caution Do not use for measurements within Categories II, III, or IV.

Note Measurement Categories CAT I and CAT O (Other) are equivalent. These test and measurement circuits are not intended for direct connection to the MAINS building installations of Measurement Categories CAT II, CAT III, or CAT IV.

Environmental

Table 48. Environmental Characteristics
PCI/PXI operating temperature	0 ºC to 55 ºC
USB operating temperature	0 ºC to 45 ºC
Storage temperature	-20 ºC to 70 ºC
Humidity	10% RH to 90% RH, noncondensing
Maximum altitude	2,000 m
Pollution Degree	2
Indoor use only.

Shock and Vibration (PXI Only)

Table 49. Shock and Vibration
Operational shock	30 g peak, half-sine, 11 ms pulse (Tested in accordance with IEC 60068-2-27. Test profile developed in accordance with MIL-PRF-28800F.)
Random vibration, operating	5 Hz to 500 Hz, 0.3 g_rms
Random vibration, nonoperating	5 Hz to 500 Hz, 2.4 g_rms (Tested in accordance with IEC 60068-2-64. Nonoperating test profile exceeds the requirements of MIL-PRF-28800F, Class 3.)

Safety Compliance Standards

This product is designed to meet the requirements of the following electrical equipment safety standards for measurement, control, and laboratory use:

IEC 61010-1, EN 61010-1
UL 61010-1, CSA C22.2 No. 61010-1

Note For safety certifications, refer to the product label or the Product Certifications and Declarations section.

EMC Standards

This product meets the requirements of the following EMC standards for electrical equipment for measurement, control, and laboratory use:

EN 61326-1 (IEC 61326-1): Class A emissions; Basic immunity
EN 55011 (CISPR 11): Group 1, Class A emissions
EN 55022 (CISPR 22): Class A emissions
EN 55024 (CISPR 24): Immunity
AS/NZS CISPR 11: Group 1, Class A emissions
AS/NZS CISPR 22: Class A emissions
FCC 47 CFR Part 15B: Class A emissions
ICES-001: Class A emissions

Note In the United States (per FCC 47 CFR), Class A equipment is intended for use in commercial, light-industrial, and heavy-industrial locations. In Europe, Canada, Australia and New Zealand (per CISPR 11) Class A equipment is intended for use only in heavy-industrial locations.

Note Group 1 equipment (per CISPR 11) is any industrial, scientific, or medical equipment that does not intentionally generate radio frequency energy for the treatment of material or inspection/analysis purposes.

Note For EMC declarations and certifications, and additional information, refer to the Product Certifications and Declarations section.

CE Compliance

This product meets the essential requirements of applicable European Directives, as follows:

2014/35/EU; Low-Voltage Directive (safety)
2014/30/EU; Electromagnetic Compatibility Directive (EMC)
2011/65/EU; Restriction of Hazardous Substances (RoHS)

Product Certifications and Declarations

Refer to the product Declaration of Conformity (DoC) for additional regulatory compliance information. To obtain product certifications and the DoC for NI products, visit ni.com/product-certifications, search by model number, and click the appropriate link.

Environmental Management

NI is committed to designing and manufacturing products in an environmentally responsible manner. NI recognizes that eliminating certain hazardous substances from our products is beneficial to the environment and to NI customers.

For additional environmental information, refer to the Engineering a Healthy Planet web page at ni.com/environment. This page contains the environmental regulations and directives with which NI complies, as well as other environmental information not included in this document.

EU and UK Customers

Waste Electrical and Electronic Equipment (WEEE)—At the end of the product life cycle, all NI products must be disposed of according to local laws and regulations. For more information about how to recycle NI products in your region, visit ni.com/environment/weee.

电子信息产品污染控制管理办法（中国RoHS）

中国RoHS— NI符合中国电子信息产品中限制使用某些有害物质指令(RoHS)。关于NI中国RoHS合规性信息，请登录 ni.com/environment/rohs_china。(For information about China RoHS compliance, go to ni.com/environment/rohs_china.)