Allen-Bradley FLEX I/O and FLEX I/O-XT — Selection Guide (Bulletin 1794) (1794-SG002)

Q: How many I/O modules can I fit on one FLEX I/O adapter?

A FLEX I/O adapter hosts exactly 8 terminal bases — up to 256 digital I/O points or 96 analog channels per adapter. That's a fixed ceiling; you can't expand it on the same adapter. To scale beyond 8 bases you add another adapter on its own network drop. This is one of the major differences between FLEX I/O (8 modules, horizontal-mount) and POINT I/O (13 – 17 modules, vertical-mount).

Q: What's the difference between FLEX I/O and POINT I/O?

Both are Rockwell distributed-I/O families with the same network-adapter options, but they have different form factors and densities. FLEX I/O (Bulletin 1794) is horizontal-mount with 8 – 32 points per module and up to 8 modules per adapter (256 digital / 96 analog points). POINT I/O (Bulletin 1734) is vertical-mount with 1 – 8 points per module and 13 – 17 modules per adapter. FLEX is the older, higher-density platform for panel-style installations; POINT is smaller and granular for just-what-you-need builds.

Q: What's the difference between FLEX I/O and FLEX I/O-XT?

FLEX I/O-XT modules are conformal coated and rated for extended temperature and harsh chemical environments. Operating range is -20…+70 °C (vs 0…+55 °C for standard FLEX I/O). The coating meets ANSI/ISA-S71.04 G1/G2/G3, IEC 6065A-4 Class 1 & 2, UL 746E, and MIL-I-46058C tropicalization standards — protecting against H₂S, SO₂/SO₃, hydrocarbons, NOₓ, wet/dry chlorine, and ammonia. Electrical specs and I/O ratings are otherwise identical between the standard and XT versions of the same catalog.

Q: Which terminal base do I need for my FLEX I/O module?

For 8- and 16-point digital modules the default base is 1794-TB3 (screw clamp) or 1794-TB3S (spring clamp) — it provides +V and common rails on every terminal, which is ideal for 3-wire sensor wiring. For 32-point modules and the 1794-IB16D diagnostic module, use 1794-TB32 / TB32S. For the 1794-IT8 thermocouple and 1794-IRT8 combo RTD/TC, use 1794-TB3T / TB3TS with the cold-junction compensation references. For AC output fuse protection, use 1794-TBNF (fused NEMA).

Q: Do I need a 1794-PS13 or 1794-PS3 for my FLEX I/O system?

Sum the 24V DC current draw of your adapter plus any modules that take backplane-fed 24V DC. The 1794-PS13 supplies 1.3 A (36 W real, 90 VA transformer load) — sufficient for up to four adapters at their 23 A / 2 ms inrush spec. The 1794-PS3 supplies 3.0 A (86 W real, 250 VA transformer) and drives up to six adapters. If you need more than 3 A, use a 1606 switched-mode supply (up to 40 A at 24V DC) or any other 19.2…31.2V DC source meeting the inrush requirement.

Q: Can FLEX I/O support Device Level Ring (DLR) topology?

Yes — use the 1794-AENTR (standard) or 1794-AENTRXT (extended-temp) dual-port EtherNet/IP adapter. Both have two RJ45 ports that participate in a DLR ring, giving single-fault-tolerant EtherNet/IP. Connect via 1783-ETAP taps along with other DLR-capable devices (ControlLogix 1756-EN2TR, PanelView, other AENTR-equipped FLEX or POINT I/O nodes). The single-port 1794-AENT / AENTK does not support DLR.

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Specifications

System Capacity

Terminal bases per adapter	Up to 8 (one adapter hosts up to 8 I/O modules)
Maximum digital I/O points per adapter	256
Maximum analog I/O channels per adapter	96
Mix of I/O	Digital, analog, temperature (RTD / thermocouple), counter, relay — freely mixed on a single adapter
Network backplane	FLEXBus — adapter converts 24V DC field power to internal backplane supply
System expansion	1794-CE1 (0.3 m / 1 ft) or 1794-CE3 (0.9 m / 3 ft) extender cables split the system into two rows / mix of orientations

Module Features

Removal and Insertion Under Power (RIUP)	Supported on every module (non-hazardous locations)
Field wiring	Lands on the terminal base, not the module — swap modules without disturbing wiring
Adjustable keyswitch	On each terminal base, prevents incorrect module insertion into a pre-configured base
Termination styles	Screw-clamp, spring-clamp, cage-clamp, D-shell, knife-disconnect, fused NEMA
Protected outputs (P)	Electronic shutdown on short, overload, over-temp; auto-recovery; no fault status to processor
Electronic-fused outputs (EP)	Open on fault; reset via push-button, software, or power cycle; fault status reported to processor
Diagnostic modules (D)	Detect open wire/device, shorted wire/device, reverse user-supply polarity
Input filter times	Selectable <1…60 ms (digital); 0…7 selector with 0 = 0.25 ms (DC) or 8 ms (AC) default
LEDs	Per-channel status for input or output state
Isolated I/O available	Yes — 1794-IA8I, 1794-OA8I for motor-control-center style applications
Conformal-coated variants	'K' suffix (e.g. 1794-IA16K) — ANSI/ISA-S71.04 G1/G2/G3, IEC 6065A-4 Class 1 & 2, UL 746E
Extended-temperature variants	'XT' suffix (e.g. 1794-IB16XT) — FLEX I/O-XT, rated -20…+70 °C, standard conformal coating

General FLEX I/O & FLEX I/O-XT Specifications

Temperature, operating (standard FLEX I/O)	0…+55 °C (32…131 °F) — varies per catalog
Temperature, operating (FLEX I/O-XT)	-20…+70 °C (-4…+158 °F)
Temperature, nonoperating	-40…+85 °C (-40…+185 °F)
Relative humidity	5…95% noncondensing
Shock, operating	30 g peak, 11 (±1) ms pulse — requires DIN rail locks
Shock, nonoperating	50 g peak, 11 (±1) ms pulse
Vibration	5 g @ 10…500 Hz (IEC 68-2-6)
Wire size	0.34…2.5 mm² (22…12 AWG) stranded copper, 75 °C rated, 1.2 mm insulation max
FLEX I/O-XT conformal coating	ANSI/ISA-S71.04-1985 G1/G2/G3; CEI IEC 6065A-4 Class 1 & 2; UL 746E; MIL-I-46058C / ASTM-G21 (tropicalization, fungicide)
Mounting	35 mm DIN rail (primary); 1794-NM1 panel-mount kit (no DIN rail); horizontal or vertical orientation

Communication Adapter Specifications (EtherNet/IP)

I/O module capacity (all FLEX adapters)	8 terminal bases
1794-AENT / AENTK	10/100 Mbps single-port RJ45; 550 mA (440 mA @ 24V DC); 7.3 W max dissipation; 0…55 °C
1794-AENTR	10/100 Mbps dual-port RJ45 (DLR capable); 500 mA max @ 24V DC; 7.1 W; 0…55 °C
1794-AENTRXT	10/100 Mbps dual-port DLR; 400 mA @ 24V DC; 6.1 W; extended temp -25…+70 °C (-13…+158 °F)
Operating voltage range	19.2…31.2V DC (includes 5% AC ripple)
Dimensions (H×W×D)	AENT/AENTK: 87×94×69 mm (3.4×3.7×2.7 in); AENTR/AENTRXT: 87×94×92 mm (3.4×3.7×3.6 in)
Weight	AENT: 179 g (6.31 oz); AENTR: 227 g (8.01 oz)

Communication Adapter Specifications (ControlNet, DeviceNet, Remote I/O, PROFIBUS DP)

1794-ACN15 / ACN15K (ControlNet, single)	5 Mbps; 7.9 W @ 24V; 23 A for 2 ms inrush; 330 mA @ 24V DC; 0…55 °C
1794-ACNR15 / ACNR15XT (ControlNet, redundant)	5 Mbps, dual coax (1786-RG6 cable); ACNR15XT rated -25…+70 °C
1794-ADN / ADNK (DeviceNet)	125 / 250 / 500 kbit/s autoselect; Allen-Bradley pin connector 942029-03
1794-ASB / ASB2 (Remote I/O / Universal Remote I/O)	57.6 / 115.2 / 230.4 kbit/s on Belden 9463; ASB = 8 modules, ASB2 = 2 modules; 7.9 W / 4.2 W
1794-APB (PROFIBUS DP)	57.6 / 115.2 / 230.4 kbit/s; 9-pin D-sub; 7.9 W; 450 mA @ 24V DC; 0…55 °C
1794-APBDPV1 (PROFIBUS DPV1)	All rates up to 12 Mbps; 9-pin D-sub; 9.6 W; 640 mA @ 24V DC
Isolation voltage	Tested 850V DC for 1 s (user power to system); 850V DC for 60 s on APBDPV1 PROFIBUS-to-backplane

Terminal Bases

Current capacity, max	10 A
Wire size (standard bases)	0.34…3.3 mm² (22…12 AWG) solid or stranded copper, 75 °C rated, 1.2 mm insulation max
Wire size (grounded / temperature bases)	0.21…1.3 mm² (24…16 AWG) stranded copper, 105 °C rated
Standard 16-point bases	1794-TB2 (generic 2-wire), 1794-TB3 (16 I/O + 18 common + 18 +V, for 3-wire sensors), 1794-TB3S (spring-clamp variant)
32-point bases	1794-TB32 (cage clamp) and 1794-TB32S (spring clamp) — required for 32-point modules and the 1794-IB16D
Grounded-analog bases	1794-TB3G (screw-clamp, 10 chassis-ground terminals) and 1794-TB3GS (spring-clamp)
Temperature bases	1794-TB3T / TB3TS — cold-junction references for the 1794-IT8 and 1794-IRT8 (thermocouple mode); 10 A on V/COM, 2 A on I/O terminals
NEMA-style bases	1794-TBN (large-gauge with I/O cover) and 1794-TBNF (8× 5×20 mm fuses for AC output modules)
D-shell bases	1794-TB37DS (37-pin) and 1794-TB62DS (62-pin) for mass-terminated panels
Conformal-coat variants	'K' suffix (TB3K, TB3SK, TB32K, TB32SK, TB3GK, TB3GSK, TBNK) — compatible with -XT modules
Dimensions (H×W×D)	94×94×69 mm (3.7×3.7×2.7 in) standard; D-shell bases 127×94×69 mm (5.0×3.7×2.7 in)

FLEX I/O Power Supplies (120V/220V AC → 24V DC)

1794-PS3 / PS3K	3.0 A output (2.8 A max at non-horizontal orientations); 86 W real / 205 VA apparent / 250 VA transformer load; drives up to six adapters; 87×94×69 mm
1794-PS13 / PS13K	1.3 A output; 36 W real / 53 VA apparent / 90 VA transformer load; drives up to four adapters; 87×69×69 mm
Output voltage	24V DC nominal
Surge current (both)	Sufficient for adapter inrush of 23 A for 2 ms each
Alternative supplies	1606 switched-mode supplies up to 40 A @ 24V DC; any compatible 19.2…31.2V DC source
Field-power current	I/O digital modules 19.2…31.2V DC; two field-power terminals per base let you daisy-chain between adjacent bases

Catalog Number Format

How to read an Allen-Bradley 1794 catalog number. Each position encodes a specific configuration attribute.

Position

Meaning

Example

1794

Bulletin prefix for FLEX I/O / FLEX I/O-XT family

1794-IB16 → Bulletin 1794

-I / -O / -IE / -OE / -IF / -OF / -IR / -IT / -IRT / -IJ / -IP / -VHSC / -ID

Module function — I=digital input, O=digital output, IE=analog input (standard), OE=analog output, IF=analog input (isolated / HART), OF=analog output (isolated), IR=RTD input, IT=thermocouple input, IRT=combo RTD/TC, IJ/IP=pulse/counter, VHSC=very high-speed counter, ID=incremental encoder

-IE8 = 8-channel non-isolated analog input; -IR8 = 8-channel RTD

A / B / C / G / H / M / V

Signal type / voltage — A=120V AC, B=24V DC sinking, C=48V DC, G=5V DC, H=125V DC, M=240V AC, V=24V DC sourcing

IA8 = 120V AC input; IB16 = 24V DC sinking input; IM8 = 240V AC input

Point count (8 / 16 / 32)

Number of channels per module

IB8 = 8 pts; IB16 = 16 pts; IB32 = 32 pts (32-pt modules require 1794-TB32 base)

Combo designators (e.g. IB10XOB6, IF2XOF2I)

Input/output combo — digits before/after the X are input/output counts

1794-IB10XOB6 = 10 inputs + 6 outputs; 1794-IF2XOF2I = 2-in + 2-out isolated analog

D / E / EP / I / P / K / XT / H

Suffix variant — D=Diagnostic, E=Electronic, EP=Electronically Protected (fused), I=Isolated, P=Protected outputs, K=Conformal coat, XT=Extended temperature, H=HART-capable (analog)

1794-IB16D = diagnostic 16-in; 1794-OB8EP = 8-out electronic-fused; 1794-IA8I = 8-in isolated; 1794-OB16PXT = 16-out protected XT; 1794-IE8H = HART-capable analog

Adapter codes

Network adapters in place of I/O codes — AENT/AENTR/AENTRXT (EtherNet/IP), ACN15/ACNR15/ACNR15XT (ControlNet), ADN (DeviceNet), ASB/ASB2 (Remote I/O), APB/APBDPV1 (PROFIBUS DP)

1794-AENTR = EtherNet/IP dual-port adapter (DLR)

Communication Protocols

Supported industrial networks and field buses for the products covered by this publication.

EtherNet/IP 1794-AENT / AENTK (single-port) or 1794-AENTR / AENTRXT (dual-port, DLR-capable). 10/100 Mbps. Connects to ControlLogix or CompactLogix via 1756-ENBT / EN2TR. ControlNet 1794-ACN15 (single) or 1794-ACNR15 / ACNR15XT (redundant coax). 5 Mbps. Allen-Bradley 1786-RG6 coax cable. DeviceNet 1794-ADN / ADNK. Autoselect 125 / 250 / 500 kbit/s. Open low-level network for simple field devices. Remote I/O (Universal) 1794-ASB (8 modules) or 1794-ASB2 (2 modules, used with PLC-5/15 or PLC-5/25 processors). Belden 9463 twinax. 57.6 / 115.2 / 230.4 kbit/s. PROFIBUS DP 1794-APB — 57.6 / 115.2 / 230.4 kbit/s; 9-pin D-sub. PROFIBUS DPV1 1794-APBDPV1 — all rates up to 12 Mbps; 9-pin D-sub. Third-party networks PartnerNetwork adapters available for RS-232 / RS-422 / RS-485, Serial / DF1, and Modbus.

Certifications & Compliance

UL Listed Industrial Control Equipment UL Listed for Class I Division 2 Groups A, B, C, D Hazardous Locations CE Marked (all applicable EU directives) UKCA marked (all applicable UK Statutory Instruments) UKEX — Explosive atmospheres ATEX — II 3 G Ex ec IIC T4 Gc (Zone 2) IECEx — IEC 60079 series RCM — Australia / New Zealand RoHS compliant TÜV certification Morocco, CCC (China), KC (Korea) Marine certification SIL 2 certification (select modules) ODVA (DeviceNet / EtherNet/IP) and ControlNet International conformance FLEX I/O-XT additional: ANSI/ISA-S71.04-1985 G1/G2/G3, CEI IEC 6065A-4 Class 1 & 2, UL 746E, MIL-I-46058C / ASTM-G21

Document Contents

Full PDF covers the following topics in detail:

FLEX I/O and FLEX I/O-XT family overview — adapter, terminal base, I/O module architecture
General system specifications and comparison table (FLEX I/O vs FLEX I/O-XT)
Specify-a-system workflow — adapter → module → terminal base → power → accessories
Communication adapter selection — EtherNet/IP, ControlNet, DeviceNet, Remote I/O, PROFIBUS DP
Device Level Ring (DLR) topology example with 1794-AENTR and 1783-ETAP taps
Digital I/O module summary and electrical-range tables (120V AC, 220V AC, 24V DC, 48V DC, 5V DC, 125V DC, relay)
Selectable input filter times — AC modules (Table 8) and DC modules (Table 9)
Module specifications tables — digital, analog, temperature, counter
FLEX I/O analog, thermocouple, and RTD modules
FLEX I/O analog output modules
FLEX I/O counter modules (1794-VHSC, IJ2, IP4, ID2)
Terminal base selection matrix — TB2, TB3, TB3S, TB32, TB3T, TBN, TBNF, TB37DS, TB62DS
Power supply selection — 1794-PS3, 1794-PS13 and transformer sizing
Optional accessories — 1794-CE1 / CE3 extender cables, 1794-NM1 mounting kit, 1492-EA35 DIN rail locks, 1794-LBL label kit
Mounting requirements — DIN rail, panel mount, horizontal / vertical orientation

Frequently Asked Questions

How many I/O modules can I fit on one FLEX I/O adapter?

A FLEX I/O adapter hosts exactly 8 terminal bases — up to 256 digital I/O points or 96 analog channels per adapter. That's a fixed ceiling; you can't expand it on the same adapter. To scale beyond 8 bases you add another adapter on its own network drop. This is one of the major differences between FLEX I/O (8 modules, horizontal-mount) and POINT I/O (13 – 17 modules, vertical-mount).

What's the difference between FLEX I/O and POINT I/O?

Both are Rockwell distributed-I/O families with the same network-adapter options, but they have different form factors and densities. FLEX I/O (Bulletin 1794) is horizontal-mount with 8 – 32 points per module and up to 8 modules per adapter (256 digital / 96 analog points). POINT I/O (Bulletin 1734) is vertical-mount with 1 – 8 points per module and 13 – 17 modules per adapter. FLEX is the older, higher-density platform for panel-style installations; POINT is smaller and granular for just-what-you-need builds.

What's the difference between FLEX I/O and FLEX I/O-XT?

FLEX I/O-XT modules are conformal coated and rated for extended temperature and harsh chemical environments. Operating range is -20…+70 °C (vs 0…+55 °C for standard FLEX I/O). The coating meets ANSI/ISA-S71.04 G1/G2/G3, IEC 6065A-4 Class 1 & 2, UL 746E, and MIL-I-46058C tropicalization standards — protecting against H₂S, SO₂/SO₃, hydrocarbons, NOₓ, wet/dry chlorine, and ammonia. Electrical specs and I/O ratings are otherwise identical between the standard and XT versions of the same catalog.

Which terminal base do I need for my FLEX I/O module?

For 8- and 16-point digital modules the default base is 1794-TB3 (screw clamp) or 1794-TB3S (spring clamp) — it provides +V and common rails on every terminal, which is ideal for 3-wire sensor wiring. For 32-point modules and the 1794-IB16D diagnostic module, use 1794-TB32 / TB32S. For the 1794-IT8 thermocouple and 1794-IRT8 combo RTD/TC, use 1794-TB3T / TB3TS with the cold-junction compensation references. For AC output fuse protection, use 1794-TBNF (fused NEMA).

Do I need a 1794-PS13 or 1794-PS3 for my FLEX I/O system?

Sum the 24V DC current draw of your adapter plus any modules that take backplane-fed 24V DC. The 1794-PS13 supplies 1.3 A (36 W real, 90 VA transformer load) — sufficient for up to four adapters at their 23 A / 2 ms inrush spec. The 1794-PS3 supplies 3.0 A (86 W real, 250 VA transformer) and drives up to six adapters. If you need more than 3 A, use a 1606 switched-mode supply (up to 40 A at 24V DC) or any other 19.2…31.2V DC source meeting the inrush requirement.

Can FLEX I/O support Device Level Ring (DLR) topology?

Yes — use the 1794-AENTR (standard) or 1794-AENTRXT (extended-temp) dual-port EtherNet/IP adapter. Both have two RJ45 ports that participate in a DLR ring, giving single-fault-tolerant EtherNet/IP. Connect via 1783-ETAP taps along with other DLR-capable devices (ControlLogix 1756-EN2TR, PanelView, other AENTR-equipped FLEX or POINT I/O nodes). The single-port 1794-AENT / AENTK does not support DLR.

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Allen-Bradley FLEX I/O and FLEX I/O-XT — Selection Guide (Bulletin 1794)