The Omron CJ1W-PRM21, also cataloged as the CJ1W-PRM21 Remote I/O Communication Unit, operates as a dedicated hardware component for PROFIBUS DP master interface execution within Omron CJ-series and NJ-series controller platforms.

Technical Identifier Matrix

• Base Part Number: CJ1W-PRM21
• Brand: Omron
• Classification: CPU Bus Unit
• Unit Version: 3.0
• Unit Address Range: 0 to F (Hex)

Hardware Specifications

Backplane Bus Velocity & Firmware Compatibility

The Omron CJ1W-PRM21 interfaces directly across the high-speed CPU bus, executing deterministic master cycle exchanges with up to 125 slave devices without introducing scan latency to the primary CPU. Internal memory allocation transfers cyclic I/O blocks dynamically between the PROFIBUS fieldbus layer and the controller memory tables during the hardware refresh phase.

Firmware version 3.0 supports both PROFIBUS DP-V1 Class 1 cyclic parameter mapping and Class 2 acyclic messaging. Galvanic isolation between the internal CPU backplane electronics and the field-side RS-485 transceiver stage isolates high-voltage electrical transients, maintaining backplane stability and preventing backplane bus noise interference across dense I/O racks.

Package Contents & Ordering Information

• 1x Omron CJ1W-PRM21 Remote I/O Communication Unit
• 1x Hardware Installation Sheet

Field Installation Guidelines

• Rack Mounting: Slide the CJ1W-PRM21 unit into the designated CPU Rack or Expansion Rack slot until the upper and lower locking tabs click into position.
• Address Configuration: Set the CPU Bus Unit rotary switch (0 to F Hex) on the front panel to establish the internal backplane device address prior to powering the rack.
• Connector Termination: Wire the RS-485 network via a standard 9-pin sub-D PROFIBUS connector (#4/40 UNC threads) equipped with an integrated EN50170 bus terminating resistor network.
• Shielding and Grounding: Terminate the PROFIBUS cable braid shield through 360-deg grounding clamps at the connector shell to establish low-impedance grounding directly to the functional earth (FE) rail.

Frequently Asked Questions

• What is the maximum current consumption of the CJ1W-PRM21 module?

  The unit draws a maximum of 400 mA at 5 VDC directly from the internal CPU rack backplane power supply.

• How many PROFIBUS slave devices can a single CJ1W-PRM21 master control?

  A single CJ1W-PRM21 master unit supports up to 125 slave devices across an address range of 0 to 125.

• What physical port interface is provided for fieldbus connection?

  The module provides a galvanically isolated RS-485 interface via a standard 9-pin sub-D female connector with #4/40 UNC threads.

• Can the CJ1W-PRM21 be installed on an NJ-series Controller Rack?

  Yes, up to 16 CJ1W-PRM21 units can be configured per NJ-series Controller Unit across CPU and Expansion Racks.

• Is the PROFIBUS field network galvanically isolated from the controller backplane?

  Yes, the RS-485 PROFIBUS transceiver circuit is galvanically isolated from the CPU backplane logic.

• How is bus termination handled on the CJ1W-PRM21 PROFIBUS line?

  Bus termination according to EN50170 standards must be provided via an external terminating resistor switch built into the 9-pin sub-D cable connector.

• Is hot-swapping permitted for the CJ1W-PRM21 unit during live operation?

  No, power to the CPU Rack and Expansion Racks must be completely isolated before inserting or removing the unit.

• What PROFIBUS protocol standards are supported by unit version 3.0?

  Unit version 3.0 supports EN50170 Volume 2 standards, covering PROFIBUS DP and DP-V1 Class 1 and Class 2 Master modes.