A20B-8100-0381 Fanuc PCB Board A20B81000381 A2OB-8IOO-O38I

FANUC A20B-8100-0381 | I/O Link II SAVE B PCB — Slave / Master Configurable Fieldbus Board, For Series 16i / 18i / 21i-A & Power Mate i-D/H, A20B-8100 Series, Japan Origin

Part Number: A20B-8100-0381

Manufacturer: FANUC Corporation (Japan)

Product Category: PCB — I/O Link II Option Board (Fieldbus Interface)

Series: A20B-8100 — FANUC i-series option PCB family

Overview

The FANUC A20B-8100-0381 is the I/O Link II interface board — the hardware that adds FANUC's proprietary OPCN-1 (formerly JPCN-1) fieldbus capability to i-series CNC controllers and Power Mate motion controllers.

It enables direct communication between the CNC and a distributed network of I/O modules, drives, and other OPCN-1 certified devices over the I/O Link II bus, independent of the standard I/O Link architecture that most FANUC CNC controllers already include as a built-in function.

I/O Link II is a different and more capable protocol than the original FANUC I/O Link.

The original I/O Link connects the CNC to FANUC's own I/O Unit-A and I/O Unit-B distributed I/O hardware in a master-slave architecture. 

I/O Link II is based on the OPCN-1 open fieldbus standard defined by the Japan Electrical Manufacturers' Association, which means I/O Link II-compatible devices extend well beyond FANUC's own I/O hardware to include any OPCN-1 certified products from third-party manufacturers.

This compatibility with OPCN-1 certified equipment expands the range of devices that can be integrated directly into the CNC system's machine control architecture.

The A20B-8100-0381 board serves both the standalone Series 16i/18i/21i-A and the Power Mate i-D/H motion controller platform.

In the Power Mate i-D/H context, this board is specifically designated as the I/O Link-II Slave Board B, reflecting the Power Mate i-D/H's role as a distributed axis controller that functions as a slave on the I/O Link II network managed by a master CNC.

Key Specifications

I/O Link II — What It Is and Why It Matters

FANUC's original I/O Link connects the CNC to FANUC's own distributed I/O units over a proprietary serial bus. It works reliably within FANUC's own product ecosystem but is limited to FANUC's I/O hardware.

I/O Link II takes a different approach. The protocol is built on OPCN-1, an open fieldbus standard developed by JEMA (Japan Electrical Manufacturers' Association). OPCN-1 certification is a verifiable compliance standard — any device that passes OPCN-1 certification can interoperate with any other certified device on the same network.

This means that on an I/O Link II network, FANUC's CNC can exchange data with OPCN-1 certified I/O terminals, sensors, drives, and other devices from a variety of manufacturers, not just FANUC's own hardware.

For machine builders and system integrators, I/O Link II opens up integration possibilities that the original I/O Link cannot provide. Specialised I/O hardware — safety relays with OPCN-1 certification, valve terminals, sensor blocks — can communicate directly with the CNC over the I/O Link II bus.

The CNC's PMC (Programmable Machine Controller) reads the status of these devices and commands them exactly as it would with native FANUC I/O, with no additional gateway hardware required.

Setting Pin SH1 — Master and Slave Configuration

The A20B-8100-0381 board carries a setting pin (SH1) that determines whether the board operates as an I/O Link II master or slave. This is an important configuration point:

Slave mode: The CNC's main I/O Link II board acts as a slave to a master station.

When the board is installed in a Power Mate i-D/H controller, it is always configured as a slave (the Power Mate acts as a distributed slave axis controller on the I/O Link II network of a higher-level master CNC). 

The plug is installed on the SLAVE side and must not be moved in the Power Mate i-D/H application.

Master mode: When installed in a standalone 16i/18i/21i-A controller for the master station function — where the CNC is the master of the I/O Link II network and OPCN-1 slave devices are connected to it — the setting pin is moved to the MASTER side.

The setting pin position must be correct for the specific application.

An incorrect setting causes I/O Link II communication failures that appear as network alarms on the CNC.

Status LED Diagnostics

The A20B-8100-0381 provides six status LEDs — four green and two red — that display the board's operational state in real time:

Green LEDs:

• RUN — Board is powered and the processor is executing normally.
• COM — I/O Link II communications are active.
• SO — Status output; reflects the network communication state.
• SLV — Slave status indicator (illuminated when operating in slave mode with valid network communication).

Red LEDs:

• TER — Terminal error; indicates an issue with the board's TBA terminal block connections.
• PRT — Protocol error; a network-level communication fault on the I/O Link II bus.

During commissioning, monitoring these LEDs confirms that the board has established communication with all configured I/O Link II slave devices.

During troubleshooting, the pattern of illuminated and extinguished LEDs narrows the fault location to the board, the network wiring, or a specific connected device.

FAQ

Q1: What is the difference between the I/O Link II board (A20B-8100-0381) and the standard I/O Link interface built into most FANUC CNC main boards?

The standard I/O Link (JD44A or similar connector on the main board) communicates with FANUC's I/O Unit-A and I/O Unit-B distributed I/O hardware. I/O Link II, enabled by the A20B-8100-0381, uses the OPCN-1 open fieldbus protocol, which is compatible with any OPCN-1 certified device including hardware from non-FANUC manufacturers.

The two systems operate independently — a CNC can use both simultaneously, with the standard I/O Link serving FANUC I/O units and I/O Link II serving OPCN-1 devices on a separate network.

Q2: The PRT (protocol error) LED is illuminated on the A20B-8100-0381. What does this indicate and how should it be diagnosed?

The PRT LED indicates a protocol-level error on the I/O Link II network — the board is not communicating correctly with devices on the bus.

First, verify the TBA terminal block wiring against the FANUC I/O Link II connection manual: check the terminating resistor at the last device in the chain, confirm correct signal polarity, and verify cable shield connections.

Next, confirm all connected devices are OPCN-1 certified and powered. 

If individual devices were recently added, confirm the CNC's I/O Link II configuration parameters reflect the current network device count and address assignments.

Q3: Can the A20B-8100-0381 be installed in any of the option slots in a 16i/18i/21i-A CNC basic unit?

Yes. For the standalone Series 16i/18i/21i-A, the I/O Link II board can be installed in any mini-slot of the 1-slot or 3-slot basic unit.

Unlike the data server board, which has specific slot restrictions, the A20B-8100-0381 has no positional constraint relative to the LCD or other boards. 

Confirm the specific unit's available slot configuration before installation.

Q4: The setting pin SH1 is installed on the SLAVE side. Can it be moved to the MASTER side in the field?

Yes, for a 16i/18i/21i-A controller where master mode is required. Move the plug from the SLAVE side to the MASTER side.

However, the Power Mate i-D/H application requires the slave side setting and the FANUC documentation explicitly states: "Do not change the setting" in this context.

Before moving the pin, verify the intended operating role of the controller. Power down the system before changing the setting pin position.

Q5: What OPCN-1 certified devices can be connected to the A20B-8100-0381 I/O Link II network?

Any device that has passed OPCN-1 (JPCN-1) certification from JEMA can be connected. This includes FANUC's own I/O Link II slave I/O units, as well as third-party OPCN-1 certified products such as distributed I/O terminals, valve manifolds, smart sensors, and certain drive systems that carry this certification.

The number of connected devices and the total data volume are governed by the I/O Link II specifications.

Consult the FANUC I/O Link II connection manual for network size limits and device configuration procedures.