1794-ASB — FLEX I/O Remote I/O Adapter Module

The 1794-ASB is a Remote I/O (RIO) adapter module for the 1794 FLEX I/O system. It connects a FLEX I/O node to a Remote I/O network — the proprietary RIO serial bus used by SLC 500 and PLC-5 controllers — allowing the FLEX I/O modules in the node to be controlled by a legacy Remote I/O master. In an age of EtherNet/IP distributed I/O, the 1794-ASB serves a specific and important role: it extends the service life of SLC 500 and PLC-5 installations by allowing modern, field-replaceable FLEX I/O modules to participate in the same RIO network without replacing the controller or the network infrastructure.

The adapter sits at the head of a FLEX I/O terminal base chain on a DIN rail. I/O modules installed on the bases to its right become available as discrete and analog I/O at a defined RIO rack/group address. From the host controller's perspective, the FLEX I/O modules appear as standard Remote I/O devices, indistinguishable from older block I/O or rack-mounted I/O at the same address.

Specifications

Parameter	Value
Part Number	1794-ASB
Platform	FLEX I/O (1794)
Network	Remote I/O (RIO) — 1770-series serial bus
Role	RIO Adapter (slave node)
Supported Controllers	SLC 500 (with 1747-SN scanner), PLC-5
Max I/O Modules per Node	8 (in one FLEX I/O node)
Baud Rates	57.6 kbps, 115.2 kbps, 230.4 kbps
Node Addressing	Rack/group address set via rotary switches on module face
Field Power	24V DC (user-supplied)
Backplane Current (5V)	500 mA max (available to FLEX I/O modules)
Connector	Blue hose (RIO cable) — screw terminals on module face
Operating Temperature	0°C to 55°C
Standards	UL 508, CE

How the ASB Adapter Works in a Legacy RIO System

Remote I/O is a serial bus topology — a single cable (the "blue hose") runs from the controller's RIO scanner module to each adapter node in sequence. Each adapter node has a unique rack/group address and responds to scan cycles from the master. The master polls each node in order, writing output data and reading input data across the entire RIO network on each scan cycle.

The 1794-ASB participates in this cycle as a standard RIO node. The FLEX I/O modules installed in its terminal base chain supply their I/O data to the adapter, which packages it into the RIO frame format and exchanges it with the master. The adapter handles all RIO protocol management — the FLEX I/O modules themselves only need to update their I/O data on the local backplane.

For facilities migrating gradually from older block I/O hardware to FLEX I/O while maintaining the RIO network and controller, the 1794-ASB is the bridge. Replace failing block I/O nodes with FLEX I/O nodes using the ASB adapter, and the controller program doesn't change — the same rack/group addresses are preserved.

FAQ

Q: Can the 1794-ASB work with a controller using EtherNet/IP instead of Remote I/O?

No. The 1794-ASB is specific to the Remote I/O serial bus. For EtherNet/IP, the 1794-AENT adapter is the correct FLEX I/O adapter. The two adapters are not interchangeable — they use completely different communication protocols and connector types.

Q: How does the 1794-ASB handle a loss of RIO communication from the master?

On communication loss, the outputs go to their configured fault state — typically de-energize (go to 0). The adapter's status LED indicates communication status. When the master re-establishes communication, normal I/O exchange resumes. The specific output fault behavior per module is configurable in RSLogix 500.

Q: What is the maximum number of 1794-ASB nodes on one RIO network?

The RIO bus supports up to 32 rack addresses (0–31) shared across all node types (block I/O, FLEX I/O, other adapters). Each 1794-ASB node occupies one rack address. The practical limit depends on how many rack addresses are already allocated to existing nodes on the network.

Q: Can the 1794-ASB be replaced with a 1794-AENT for EtherNet/IP migration without changing the FLEX I/O modules?

Yes. The FLEX I/O terminal base chain and all installed I/O modules remain in place. Replace the adapter at the head of the chain and reconfigure the modules in Studio 5000 for the EtherNet/IP architecture. The controller program addressing will change from RIO rack/group references to EtherNet/IP I/O tags, which requires program updates — but the physical I/O wiring to the field devices is preserved entirely.

1794-ASB New Factory Sealed 1794ASB Remote I/O Adapter