Introduction to Omron NJ/NX PLC Programming: Architecture and First Project

Omron NJ and NX series machine automation controllers (MAC) replace traditional fixed-memory PLC architectures with fully symbolic, tag-based IEC 61131-3 programming and native EtherCAT master synchronization. Engineered within the unified Sysmac Studio environment, they combine logic control, multi-axis motion, safety, and vision inspection inside a single deterministic execution cycle.

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Hardware and Software Specifications

Parameter	Specification	Notes
Controller Families	Omron NJ101, NJ301, NJ501, NX102, NX1P2	Dual-core Intel or ARM CPU
Engineering IDE	Sysmac Studio v1.40 or later	64-bit Windows environment
Fieldbus Protocols	EtherCAT (100 Mbps), EtherNet/IP (CIP)	Dual independent Ethernet ports
IEC 61131-3 Languages	Ladder Diagram (LD), Structured Text (ST)	Strictly type-checked
Cycle Period	500 µs – 4 ms (depending on CPU model)	Deterministic motion sync

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Core System Architecture

1. From Memory Addresses to Symbolic Variables

In legacy Omron platforms (CJ1, CJ2, CS1), memory was assigned to physical areas such as CIO 0.00, D100, or W0.00. The NJ/NX platform eliminates raw memory maps in favor of symbolic variables:

• Global Variables: Accessible across all tasks, connected HMIs, and EtherCAT network devices.
• Local Variables: Scoped strictly within their Program Organization Unit (POU) to prevent side-effects.

2. IEC 61131-3 Data Types

• Primitive types: BOOL, INT, DINT, LINT, REAL, LREAL
• Time notation: TIME (T#200ms, T#5s)
• Composite types: User-Defined Types (DUT / Structures) and multidimensional Arrays

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Step-by-Step Configuration (How-To)

Step 1: Initialize the Project

1. Open Sysmac Studio and select New Project.
2. Under Category, select Controller. Under Device, pick your CPU model (e.g., NX102-9020) and target firmware version.

Step 2: Configure the EtherCAT Network

1. Navigate to Configurations and Setup > EtherCAT in the left project tree.
2. Right-click the master controller icon and select Compare and Merge with Actual Network Configuration to automatically discover connected servo drives and slice I/O.

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Code Example: Axis Readiness and Error Reset in Structured Text

The following Structured Text snippet verifies that an EtherCAT servo axis is ready and executes a reset if an error state is active:

// Check if axis is operational and free of errors
IF (Axis01.Status.Ready AND NOT Axis01.Status.Error) THEN
    bAxisOperable := TRUE;
ELSE
    bAxisOperable := FALSE;
    // Execute reset on operator trigger
    IF (Axis01.Status.Error AND bResetTrigger) THEN
        MC_Reset(Axis := Axis01, Execute := TRUE);
    END_IF;
END_IF;

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Common Diagnostic Fault Codes

Error Code	Definition	Remediation
0x0020	Network Configuration Verification Failed	Compare hardware vendor ID and revision in Sysmac Studio against physical nameplates.
0x0031	EtherCAT Communication Timeout	Inspect cable terminations, shielding grounding, or increase the communications cycle time.

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Reference Manuals

• Omron W500: NJ/NX-series CPU Unit Software User’s Manual
• Omron W501: NJ/NX-series Instructions Reference Manual
• Omron W507: NJ/NX-series Motion Control Instructions Reference Manual