Resolving Omron CS1G Serial Connection Failures on Windows 11

Problem Overview

Engineers attempting to connect a SYSMAC CS1G-CPU PLC to a Windows 11 workstation through a third-party USB-to-serial adapter frequently receive "No response from PLC. Ensure baud rate is correct" inside CX-Programmer or a generic Timeout inside any Host Link / FINS client. The CPU is alive, the program is running, and the loopback test passes, yet the upper layer still cannot complete a frame exchange. In almost every case the failure is not a PLC fault, not a CX-Programmer fault, and not a Host Link protocol fault — it is a Windows 11 driver-binding fault on the USB bridge chip.

The most common symptom is that the USB device enumerates in Device Manager → Other devices as a generic CP2102 USB to UART Bridge Controller with a yellow warning triangle, or that a genuine CH340/CH341 cable shows USB-SERIAL CH340 (COMx) but the COM port number is unstable across reboots, leaving CX-Programmer pointing at a phantom port. The CS1G never sees the host because the virtual COM port never opens, or opens with a baud rate that the peripheral port cannot match.

Affected Hardware and Software Matrix

Reference manual for CPU operation, port pinout, and DIP switch meanings: W339 SYSMAC CS Series CS1G/H-CPU Operation Manual (PDF).

Root Cause Analysis

The CS1G peripheral port is a fixed-format 1:N Host Link slave. The CPU replies only when (a) the virtual COM port on the PC opens cleanly, (b) the baud rate / data bits / parity match the PLC port settings, and (c) the cable wires peripheral-TXD, peripheral-RXD, peripheral-RTS, and peripheral-CTS into a crossover that the Host Link driver expects. Any of three conditions, in order of frequency, will break the link on Windows 11:

1. Unsigned / mismatched USB bridge driver. Many low-cost cables ship with a CH340 or clone-CP2102 chipset. Windows 11 enforces driver signature enforcement (DSE) by default. The driver fails to bind, the device falls back into Other devices, and the COM port never appears — or appears but returns ERROR_ACCESS_DENIED on CreateFile.
2. Wrong port topology. CX-Programmer auto-detect tries the peripheral port first. If the cable is wired to the RS-232C option board (CS1W-SCB21) instead, the CPU never replies and the driver surfaces a No response from PLC error. Switching the source cable from one port to the other requires changing both the physical wiring and the Network Type in CX-Programmer.
3. Baud rate / frame mismatch. The default Host Link baud rate is 9600 / 7E2 (7 data bits, even parity, 2 stop bits). Third-party software sometimes probes at 19200 / 8N1. The CPU's peripheral port is wired for 7E2; it will not negotiate.

Omron's own position, per the W339 manual, is that the supported path is the CS1W-CIF31 mounted in the CPU's option-board slot, terminated at the PC by a CS1W-CN226 (or equivalent DE9-to-DE9 Host Link cable). The CIF31 presents itself as an Omron CS1W-CIF31 USB Serial device class with a Microsoft-signed INF, so it binds cleanly on Windows 10 and 11 without third-party driver packages.

Driver Conflict Diagnosis (Step-by-Step)

1. Open Device Manager, expand Ports (COM & LPT), then plug the cable in. If the new COM port appears, the cable is functional and you can skip to CX-Programmer configuration.
2. If the device appears under Other devices as CP2102 USB to UART Bridge Controller or USB-SERIAL CH340 with a yellow triangle, right-click → Update driver → Browse my computer for drivers. Point at the vendor's signed INF, not the Windows Update catalog.
3. If the vendor offers no signed driver, you have three choices:
   • Disable DSE temporarily with bcdedit /set testsigning on (reboot required). Acceptable for a bench PC, not for a production asset.
   • Install the WCH CH341SER package from the official WCH site, not from a forum mirror.
   • Replace the cable with the Omron CS1W-CIF31 (recommended).
4. Confirm the COM port number is stable across a power cycle. If it increments (e.g., COM3 → COM4), disable Allow the computer to turn off this device to save power on the USB root hub and check BIOS for xHCI hand-off.
5. Verify the port is open with a loopback or a HyperTerminal/PuTTY test on the host side. Send a single < (Host Link header). On a working path the CPU will respond with the unit number echo; on a broken path the read times out.

Recommended Solution: CS1W-CIF31 + CS1W-CN226

The CS1W-CIF31 is a USB-to-RS-232C option board that mounts directly into any CS1G-CPU option-board slot. It is a Class-1 peripheral board, meaning it owns the CS1G's peripheral port. The host PC sees a CDC-compliant USB serial device plus a virtual COM port, and CX-Programmer connects through the SYSMAC WAY Host Link driver without any vendor-specific configuration.

Installation procedure

1. Power down the CPU. Remove the blank option-board cover (slot 1 or slot 2 on the CPU chassis).
2. Insert the CS1W-CIF31 with the USB connector facing the front of the CPU. Torque the two mounting screws to 0.3 N·m.
3. Apply power. Windows detects Omron CS1W-CIF31 USB Serial Converter (COMx) and binds the in-box usbser.sys driver automatically — no INF required.
4. Connect CS1W-CN226 (DE9 male / DE9 female, 2 m) between the CIF31 DE9 and the host PC's serial port, or use a USB-to-DE9 pigtail if the host has no DB9.
5. Note the COM number, then move to CX-Programmer configuration.

CS1W-CIF31 DIP switch (SW1)

For a one-to-one Host Link to a single PC, all four switches remain OFF. If you later move to a 1:N Host Link on an RS-422/485 board, switch 1 goes ON only on the two end nodes.

CX-Programmer Configuration

1. Launch CX-Programmer 9.7x or later. Open or create the project for the CS1G.
2. From the PLC menu, choose Auto Online → Direct Online. CX-Programmer will scan COM1..COM256, attempt Host Link frames on each, and report which port answered.
3. If auto-connect fails, choose Change Connection Method and set:
   • Network Type: SYSMAC WAY (Host Link)
   • COM Port: the COM number reported in Device Manager
   • Baud Rate: 9600 (default for CS1G peripheral port)
   • Data Bits / Parity / Stop: 7 / Even / 2
   • Unit Number: 00 (host link address of the CPU)
   • Response Timeout: 2 s for serial (10 s is too lenient and masks driver hangs)
4. Click Test. A successful test shows Connected; a failed test shows No response. If No response persists, see the troubleshooting matrix below.
5. Once connected, the program and I/O memory are accessible; save the project and go online.

Host Link Protocol Parameters

Host Link is a simple half-duplex ASCII protocol. The CPU's peripheral port always runs as a slave; it speaks when spoken to. Defaults that matter when a link is dead:

If a previous integrator changed the baud rate to 19200 or 38400, the default 9600 probe in CX-Programmer will fail. The fix is either to re-set the PLC Setup from a known-good project (online edit) or to re-try CX-Programmer's Auto Online at the matching baud rate. The PLC Setup is held in flash; cycling power does not reset it.

Peripheral Port Pinout Reference

The CS1G peripheral port is a Hosiden TCP9520-01 4-pin mini-DIN, not a DE9. The CS1W-CIF31's DE9 connector on the CPU side, plus CS1W-CN226, gives you a DE9 on the host side. If you need a wiring diagram for a non-Omron cable, see the Pro-face CS/CJ Series HOST Link Driver reference (PDF), which documents the exact peripheral-port pinout and the DE9 crossover required for Host Link.

A straight-through DE9 cable, or any cable that does not swap RTS↔CTS, will leave the peripheral port's hardware flow control wedged. The CS1W-CN226 already implements the required crossover.

Troubleshooting Matrix

Verification Procedure

1. With CX-Programmer offline, choose PLC → Transfer → To PLC for a small, known program change (toggle a contact). If the transfer completes, the link is healthy.
2. Open the Watch Window. Add a CIO bit (e.g., CIO 100.00) and a DM word (e.g., D0). Verify values update on every PLC cycle.
3. From the host, send a Host Link RD command for DM 0000 through a PuTTY session at 9600/7E2. Expected echo:

   >00RD00000001
   <0000

   If the response is missing or corrupted, the problem is the host-side COM port or the cable, not CX-Programmer.
4. Power cycle the PC and the CS1G. Repeat the auto-online. The link should come up within 5 s.

Field-Proven Caveats and Edge Cases

• Multi-rack CS1G with several CPU units. A second CS1G with a non-zero Host Link unit number requires changing both the PLC Setup and the CX-Programmer unit-number field. Default zero on a 1:N network will collide with another node already on the bus.
• Hot-Standby CS1D. The CS1D dual-redundant CPU uses the same CIF31 driver, but only the active CPU responds on the peripheral port. While the standby CPU is initializing at power-up (up to 30 s for the duplex link), the host will time out. Lengthen CX-Programmer's Response Timeout to 5 s for CS1D stations.
• Cable sticker program. At plants with more than a handful of bench cables, sticker the cable body with its device-instance path (e.g., USB\VID_10C4&PID_EA60\5&2&1). This is the single most useful bit of evidence when a cable has been silently swapped.
• RS-422/485 option boards. If the application requires 1:N Host Link to multiple CS1G CPUs on a twisted pair, use a CS1W-SCB41 (RS-422/485) plus 120 Ω termination at both ends. The CS1W-CIF31 only does RS-232C and only supports a 1:1 topology.
• CX-Programmer on ARM64 Windows 11. CX-One 4.6x is x86/x64 only. ARM-based Surface devices cannot run it under the x64 emulator without a forced x86 install. Use an x64 Windows 11 PC for the bench.

FAQ