Configuring Omron CP1L NT Link 1:1 Communication with NS HMI

Problem Overview

An Omron CP1L CPU connected to an NS-series Programmable Terminal over NT Link 1:1 sometimes refuses to come up. The PLC accepts programs through CX-Programmer / Sysmac Studio, the CP1W-CIF01 RS-232C option board shows a faint blink on the SD/RD LEDs when the PT boots, but the PT's communication indicator never reports a healthy link, and no tags update. The same panel works on a bench test rig with a CJ2M CPU but fails on the CP1L. The root cause is almost always one of three things: the CP1L front-panel DIP switch that controls option-board detection, the protocol/speed selection in the PT's communications menu, or the wiring direction on the RS-232C null-modem cable.

This reference documents the full NT Link 1:1 commissioning flow between a CP1L and an NS HMI, with emphasis on the option-board DIP-switch behavior, NT Link speed pairing (38,400 Standard vs. 115,200 High), and verification through both LED indicators and CX-Programmer online monitor. It is based on the official Omron CP1L Operation Manual (W395) and the Omron NS-series Programmable Terminal catalog.

Hardware Architecture: CP1L, CP1W-CIF01, and NS HMI

The CP1L-L and CP1L-M CPU families expose serial ports through a combination of built-in ports and option-board slots:

The NS-series PT (NS5-SQ/NS5-TQ, NS8, NS10, NS12, NS15) ships with two serial ports, A and B. Port A is the primary RS-232C / RS-422A port on a D-sub 9-pin male; port B is RS-232C only on most models (some NS5 hardware variants ship port B as RS-422A). NT Link is supported only on port A.

For NT Link 1:1, the typical wiring is:

• CP1L built-in RS-232C port 1, or CP1W-CIF01 in Slot 1, or CP1W-CIF01 in Slot 2 — any of the three will work.
• NS HMI Serial Port A.
• RS-232C null-modem (cross-over) cable, 3-wire minimum (SD, RD, SG) plus optional RTS/CTS handshake depending on PT settings.

NT Link Protocol: 1:1 vs. 1:N Distinctions

NT Link is Omron's proprietary high-speed master/slave protocol used between CP1L/CJ2/CS1 CPUs and NS/NP-series PTs. Two modes exist:

Critical limitations to remember when configuring the PT:

• NT Link 1:1 only runs on RS-232C. RS-422A or RS-485 multidrop is supported only on NT Link 1:N. Selecting NT Link 1:N over an RS-232C link will fail because multidrop arbitration cannot function without the differential driver.
• Baud rate must match on both sides. Standard = 38,400 bps; High = 115,200 bps. There is no auto-baud. If the PLC is set to High and the PT is set to Standard, or vice versa, the PT's RD indicator will flicker briefly at boot and then go dark.
• Unit number is fixed at 0 in 1:1 mode. In 1:N, each PT must carry a unique unit number (0..N-1) that matches the PLC's port address table.

CP1L-specific NT Link timing: the high-speed mode at 115,200 bps requires the option-board slot to be operating in 4-wire full-duplex mode. The CP1W-CIF01 is full-duplex by default; the CP1W-CIF12 (RS-485) must be 2-wire / 4-wire configured by the PLC Settings menu before use.

PLC Configuration in CX-Programmer / Sysmac Studio

The CP1L serial port used by the PT must be configured for NT Link in the PLC's peripheral settings. Two parameter sets must agree: the protocol and the port.

CX-Programmer (CP1L-L, CP1L-M)

1. Connect to the CPU with PLC → Auto Online → Direct Online (USB) or via the RS-232C built-in port.
2. Open PLC → Edit → Settings → Serial Port 1 (for built-in RS-232C) or Serial Option Port 1/2 (for CP1W-CIF01 in Slot 1 or Slot 2).
3. Set Mode = NT Link 1:1 (or NT Link 1:N with the matching unit number if multidrop).
4. Set Baud Rate = 115,200 bps (High) or 38,400 bps (Standard). The PLC defaults to Host Link @ 9,600 bps; the default must be changed.
5. Transfer the new settings with Options → Transfer to PLC. The CPU will write the port parameters to flash and reinitialize the port.

Sysmac Studio (CP1L-L14DR-/CP1L-M series with newer firmware)

1. Open the project, double-click CP1L CPU Unit → Settings → Serial Port.
2. Choose the port (built-in or option slot), then Protocol = NT Link 1:1.
3. Choose Baud Rate = High (115,200) or Standard (38,400).
4. Click Apply → Transfer to Controller. Power cycle the CPU for the new settings to take effect.

PT Configuration in NS-Designer / Sysmac Studio

The NS HMI side has three settings that must agree: the port, the protocol, and the speed.

NS-Designer (legacy NS5/NS8/NS10/NS12/NS15)

1. Open the project in NS-Designer, double-click PT → System Settings → Comm.
2. Set Port A = NT Link 1:1 (or NT Link 1:N if multidrop).
3. Set Speed = High (115,200) or Standard (38,400) — must match PLC exactly.
4. Set Unit Number = 0 for NT Link 1:1; for 1:N, set each PT to a unique number 0..7.
5. Click Transfer → Send → To PT via USB or Ethernet. The PT reboots after writing the new comm settings.

Sysmac Studio (newer NS-series projects)

1. Open the HMI project in Sysmac Studio, expand HMI → Configurations → Communications.
2. Add a new connection: Driver = NT Link 1:1 on Serial Port A.
3. Match the speed to the PLC (High 115,200 or Standard 38,400).
4. Build and deploy to the PT.

The PT's System Menu → Communications screen on the device itself (offline, no CX-Programmer attached) is also configurable from the front panel. This is the fastest way to verify baud-rate pairing when the PLC and PT disagree at boot: the PT screen lists the active connection, the negotiated speed, and any comm error code.

RS-232C Wiring Between CP1W-CIF01 and NS Serial Port A

CP1W-CIF01 is a D-sub 9-pin male with the standard Omron RS-232C pinout (different from the IBM PC "AT" pinout). The NS-series Port A is also D-sub 9-pin male with the IBM PC-style pinout (RD on pin 2, SD on pin 3). A cross-over cable is therefore required.

Minimal 3-wire operation (no hardware handshake) requires only pins 2, 3, and 5 connected cross-over. For 5-wire full handshake, also connect pins 4, 5, 7, 8 cross-over. Cable length must be ≤15 m for 38,400 bps and ≤2 m for 115,200 bps per Omron W395 cable specifications.

CP1L Front-Panel DIP Switch and Option-Board Detection

The CP1L CPU ships with a small DIP-switch bank on the front face (four switches on CP1L-L10/14/20; the same physical switch bank on CP1L-M30/40/60 and CP1L-L30/40/60 covers up to four option-board slots plus peripheral enable lines). Two of these switches control how the CPU detects the CP1W-CIF01/CIF11/CIF12 option boards in Slot 1 and Slot 2:

• Slot 1 switch — ON: Option Board Slot 1 is in Auto mode. The CPU auto-detects the option-board type (RS-232C, RS-422A, or RS-485) on power-up and loads the matching driver.
• Slot 1 switch — OFF (default): Slot 1 is in Setup mode. The CPU does not auto-detect; the option-board type and protocol must be declared explicitly through the PLC Settings dialog and persisted with a power cycle.
• Slot 2 switch: Same behavior for Slot 2.

The behavior seen by the integrator in the field is exactly what gets reported most often: in Auto mode the CPU keeps the port hot and responds to PT polling as soon as the PT is online; in Setup mode the CPU responds after a PLC Settings transfer and power-cycle, but a subsequent PT reboot or PLC power-cycle can cause the link to drop because the option-board firmware falls back to its default (Host Link @ 9,600 bps), which does not match NT Link @ 38,400 or 115,200. The CP1W-CIF01 RD/SD LEDs will flicker briefly on the first PT poll attempt because the PT is sending frames at the wrong baud rate and the PLC is rejecting them, but the link never stabilizes.

Recommended setting for NT Link 1:1 with the CP1W-CIF01:

1. Set the Slot 1 DIP switch to ON (Auto) if the CP1W-CIF01 is in Slot 1.
2. Set the Slot 2 DIP switch to ON (Auto) if the CP1W-CIF01 is in Slot 2.
3. Power cycle the CP1L and verify the option board is detected.

If Auto mode is unavailable or the application demands explicit protocol control (for example, when a slot is being shared between Host Link to a SCADA and NT Link to a PT through a multiplexer), set the DIP switch to OFF (Setup) and verify that the option-board protocol, baud rate, and unit number are written to flash and that a power-cycle reload happens between any PT reboot and the next PLC scan. A field-proven heuristic is: leave the DIP switch in its factory default (OFF / Setup) and explicitly configure NT Link 1:1 through the PLC Settings dialog with the same baud rate on both sides. Toggling the switch into Auto mode after the slot has been used in Setup mode can leave the option-board firmware in a half-configured state until a full power-cycle clears it.

Step-by-Step Commissioning Procedure

1. Pre-power checks. Confirm the CP1W-CIF01 is fully seated in the chosen slot. Verify the slot cover screw is torqued (CP1L option boards are not hot-swappable).
2. Set the DIP switch for the slot to the factory default (OFF / Setup). Power off the CP1L, verify the switch, restore power.
3. Connect the RS-232C cross-over cable from the CP1W-CIF01 D-sub to NS Port A. Verify the cable with a continuity tester if any pins are uncertain.
4. Configure the PLC. In CX-Programmer, set Serial Option Port 1 (or Serial Port 1 for the built-in RS-232C) to NT Link 1:1, High 115,200 bps (or Standard 38,400 if the cable run exceeds 2 m). Transfer to PLC, then power-cycle the CPU.
5. Configure the PT. In NS-Designer or directly on the PT's offline menu, set Port A to NT Link 1:1, speed High (or Standard), unit number 0. Transfer the project and reboot the PT.
6. Verify the link from the PT. From the PT's System Menu, open Communications → Status. The link should report Online within 3-5 seconds. If it reports Offline or Comm Error 0x01, jump to the troubleshooting matrix below.
7. Verify from the PLC. In CX-Programmer, go online and check PLC → Monitor → Communications → Serial Port status. Active NT Link traffic appears as a continuously incrementing frame counter.
8. Bind a tag. Add a numeric display on the PT bound to D0 or W0. Force D0 = 12345 in CX-Programmer. Confirm the PT updates within 1 second.

LED Diagnostics and Link Verification

Diagnostic sequence when the PT reports Offline:

1. Open the PT's System Menu → Communications. The protocol, speed, and unit number will be shown. Confirm they match the PLC.
2. Press Test → Loopback on the PT (if available on the firmware). If the loopback passes but the link still fails, the cable or PLC is at fault.
3. On the PLC, monitor A392.05 (CP1L peripheral port busy) and A392.06 (option-port comm error) — these give a coarse fault code.
4. Connect a serial-line analyzer (e.g., a Wireshark on a USB-RS232 adapter with an Omron NT-Link decoder) between the PLC and PT to capture the actual frames. NT Link polls begin with byte 0x00, unit 0x00, command 0x0A.

Troubleshooting Matrix

FAQ