Omron CJ1W-DRM21 — DeviceNet Master/Slave Unit, 63 Nodes
SKU: CJ1W-DRM21USD 125.00
CJ-series DeviceNet CPU Bus Unit that operates as both master and slave simultaneously. 500/250/125 kbps, 63-node capacity, 2,048 fixed / 16,000 user-set I/O points as master, 32/3,200 as slave. EDS-based configuration via DeviceNet Configurator software.
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Product Overview
The CJ1W-DRM21 is Omron's CJ-series DeviceNet CPU Bus Unit, the standard DeviceNet interface for connecting CJ1M / CJ2M / CJ2H / NJ-series PLCs to a DeviceNet fieldbus network. It can operate as both a DeviceNet master (controlling up to 63 slave devices) and a DeviceNet slave (exposing its own I/O to a higher-level master) simultaneously, which makes it the workhorse for hierarchical networks where a main PLC controls a DeviceNet sub-network of remote I/O blocks (DRT2 / DRT1 / GRT1 series) and AC drives (MX2 / RX-series VFDs), while also being visible to a higher-level controller (e.g., an NJ-series machine controller exposing its machine status to a plant-wide SCADA via DeviceNet).
Why DeviceNet in 2024+ when EtherNet/IP exists
DeviceNet is older (1990s ODVA standard) and slower (500 kbps max) than EtherNet/IP, but it remains dominant in three contexts: (a) Brownfield retrofits — many existing machines have DeviceNet field devices already wired, and replacing them with EtherNet/IP would require re-wiring the entire plant; (b) Cost-sensitive applications — DeviceNet slaves (DRT2-ID16 remote I/O blocks, MX2 VFDs) are typically 20-30% cheaper than EtherNet/IP equivalents, so for low-bandwidth discrete I/O applications where DeviceNet's 500 kbps is sufficient, the cost savings add up; (c) Specific industries — automotive assembly, material handling, and tier-1 OEM machines are heavy DeviceNet users for legacy reasons.
Decoding the CJ1W-DRM21 model within the DeviceNet family
The CJ1W-DRM21 is the CJ-series standard DeviceNet unit. Predecessors and alternatives: C200HW-DRM21-V1 (legacy SYSMAC C200H series, 32 nodes max, less I/O — supersedes for new designs), CS1W-DRM21 (CS-series equivalent, 63 nodes, same I/O capacity — drop-in compatible for CS-series PLCs), CS1W-DRM21-V1 (CS-series with enhanced features), CJ1W-DRM21 (this SKU, CJ-series 63 nodes), CJ1W-DRM21-V1 (later revision with minor firmware enhancements). The DR suffix stands for DeviceNet Remote I/O Master; the M21 indicates the standard master unit. For new CJ-series installations, also consider the CJ1W-EIP21 (EtherNet/IP unit, 32 CIP connections, much higher bandwidth) or the CJ1W-PNT21 (PROFINET master for European installations).
Master + slave simultaneous operation
The CJ1W-DRM21 can be both a master on one DeviceNet network and a slave on another at the same time. Practical example: a main PLC in a plant control room runs a CJ1W-DRM21 as a master for a DeviceNet sub-network of 30 remote I/O blocks (DRT2-ID16S for digital inputs, DRT2-OD16-1 for digital outputs) on a packaging line. The same PLC also reports its status to a higher-level PLC via a second DeviceNet network, where the higher-level PLC's CJ1W-DRM21 acts as master and the main PLC's CJ1W-DRM21 acts as slave. This dual-role capability is unique to the CJ1W-DRM21 and CS1W-DRM21; the older C200HW-DRM21-V1 was master-only.
Key Features
- CJ-series DeviceNet CPU Bus Unit
- Acts as both DeviceNet master AND slave simultaneously
- 63 nodes maximum
- Baud rates: 500 kbps / 250 kbps / 125 kbps
- I/O capacity as master: 2,048 points max
- I/O capacity as master: 16,000 points max
- I/O capacity as slave: 32 points max
- I/O capacity as slave: 3,200 points max
- SKU: CJ1W-DRM21
- Series: CJ1W CPU Bus Units (CJ-series specialty communications)
- Voltage: 11 TO 25 VDC
- I/O: 2 I/O
Best-Fit Applications
- Distributed I/O consolidation on a packaging machine — 30 DRT2-ID16S 16-point digital input blocks and 12 DRT2-OD16-1 16-point digital output.
- Variable-frequency drive network on a conveyor system — 12 Omron 3G3MX2-A4007-V2 VFDs connected via DeviceNet, with the CJ1W-DRM21 as master.
- Sensor / actuator junction boxes on a bottling line — 8 DRT2-MD16S mixed I/O junction boxes distributed along the line.
- Hierarchical control in a plant — bottom-level CJ1W-DRM21 acts as master for local slaves, while also being a slave to.
Buying Checklist
- Pick CJ1W-DRM21 for CJ-series DeviceNet master + slave — supports 63 nodes, 32,000 I/O points, dual-role master/slave
- Pick CS1W-DRM21 for CS-series DeviceNet — same capabilities, drop-in compatible for CS-series PLCs
- Pick CJ1W-EIP21 for EtherNet/IP — for new designs, higher bandwidth, modern alternative with 32 CIP connections
- Pick CJ1W-PNT21 for PROFINET master — for European installations requiring PROFINET-based field devices
- Pick CJ1W-PRM21 for PROFINET I/O controller — for PROFINET-based field devices
- Pick CJ1W-DRM21-V1 for the later firmware revision — minor enhancements over the original DRM21
Technical Specifications
| Model | CJ1W-DRM21 |
|---|---|
| Series | CJ1W CPU Bus Units (CJ-series specialty communications) |
| Type | DeviceNet Master + Slave Unit |
| Communications Protocol | DeviceNet (ODVA standard, CIP-based) |
| Master / Slave Capability | Both simultaneously |
| Baud Rates | 500 kbps / 250 kbps / 125 kbps (selectable via rotary switch) |
| Maximum Slave Nodes | 63 nodes |
| I/O as Master (Fixed Allocation) | 2,048 points max |
| Communications Power Supply Voltage | 11 to 25 VDC (from DeviceNet bus) |
| Current Consumption | Communications: 18 mA max; Internal circuit: 290 mA max |
| Communications Distance (Trunk) | 500 m at 125 kbps, 250 m at 250 kbps, 100 m at 500 kbps |
| Slot Type | CPU Bus Unit (not Basic I/O or Special I/O) |
| Mounting | CJ-series DIN-rail mount, occupies one slot on CJ bus (CPU rack or expansion rack) |
| Dimensions (W × H × D) | 31 × 90 × 78.7 mm |
| Operating Temperature | 0 to +55 °C |
Resources & Downloads
FAQ for CJ1W-DRM21
Can the CJ1W-DRM21 act as both a master and a slave at the same time?
Yes. The CJ1W-DRM21 (and its CS1W-DRM21 predecessor) is unique among Omron DeviceNet units in supporting dual-role master + slave simultaneously. This is configured in the DeviceNet Configurator Ver. 2.1: the master scan list defines which slaves the unit polls on its local DeviceNet network, and the slave's exposed I/O areas define which I/O points the unit exposes to a higher-level master on a separate DeviceNet network.
What's the difference between fixed allocation and user-set allocation on the CJ1W-DRM21?
Fixed allocation is the simpler DeviceNet I/O mapping: each slave's I/O is mapped to a fixed block in the CJ CPU's CIO area (e.g., slave 1 = CIO 2000, slave 2 = CIO 2001, slave 3 = CIO 2002, etc.). The mapping is automatic and predictable — you know exactly where each slave's I/O is in memory. The limitation is that the total I/O is constrained to 2,048 points as master (32 fixed blocks of 64 points each).
How do I configure the CJ1W-DRM21 with the DeviceNet Configurator?
Install the DeviceNet Configurator Ver. 2.1 (or later) on a Windows PC. Connect the PC to the DeviceNet network via a USB-to-DeviceNet interface (e.g., Omron DRT1-COM or 3G3AX-DX-EIP-COM). In the Configurator: (1) Upload the network — the tool scans the DeviceNet bus and discovers all slaves, reading their EDS files for I/O footprint.
What's the maximum number of I/O points and slaves on the CJ1W-DRM21?
The CJ1W-DRM21 supports up to 63 slave nodes per master (the DeviceNet standard maximum), with up to 2,048 I/O points using fixed allocation, or up to 16,000 I/O points using user-set allocation (using DM area words). The total per master is up to 32,000 points (2,000 words). Common slave configurations: DRT2-ID16S (16 digital inputs per slave, 16 IN consumed) → 63 slaves × 16 IN = 1,008 IN per master (well within fixed allocation limit).
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