Configuring Omron CS1G-CPU42 DeviceNet, Serial, and PID Loops

1. System Overview and Component Identification

The reference platform described here is a legacy Omron CS1 series installation centered on a CS1G-CPU42 processor. The architecture combines a DeviceNet fieldbus segment with a serial-communication board, and is representative of many field deployments that were originally commissioned a decade or more ago and are now being expanded.

2. Required Software Stack - CX-One vs. Individual Tools

Omron sells the full engineering environment as a single DVD/USB bundle called CX-One. For this project, CX-One is the correct choice over stand-alone CX-Programmer, because the DeviceNet Configurator, CX-Protocol (for SCB41 macro protocol work), and CX-Simulator all share the same installer, the same PLC registry, and the same component-version handshake. If you install CX-Programmer and the Configurator from different media, you will frequently see Specified unit can not be accessed errors when going online with the DRM21.

Omron's Digital Technical Library DVD contains every CS1, CJ1, and CS1W instruction-reference manual in PDF. Ask the local Omron rep for a copy; it is the single most valuable reference for any integrator working on a CS1G project.

3. Memory Area Management - Upload, Save, Download

Unlike Allen-Bradley Logix Designer, CX-Programmer does not store tag values inside the program file. The program file (.cxp / .cxt) contains the logic and the symbol/comment data, while the memory data is held in a separate file with the extension .mem or, more commonly, the PLC Memory view inside the project tree.

3.1 Uploading the current memory contents

1. Connect to the CS1G-CPU42 with the project offline (or online without transferring).
2. From the project tree, right-click Memory and choose Memory View.
3. Use Edit > Select All, then PLC > Upload from PLC (hot-key: F12 in some versions, or right-click > Upload). This populates the editor with the live IR, SR, AR, HR, LR, DM, EM, TIM, and CNT values.
4. Choose File > Save As and pick Memory Data as the type. The data is written into the project workspace next to the .cxp file.

3.2 Downloading the new program without losing retained values

1. Verify the saved .mem file matches the online PLC exactly by selecting PLC > Compare with PLC.
2. Go online. The Operating Mode should be set to Program before any download; on a running process, schedule a maintenance window.
3. Choose PLC > Transfer > To PLC and select Program + Memory Data (not just Program). This bundles the DM/HR/EM initial values plus the new ladder.
4. Re-enter Monitor or Run mode and verify key retentsive words (HR, DM area D0..D32767, EM banks E0_0..E0_32767 if present) with the upload comparison from step 1.

4. CS1W-SCB41-V1 Serial Communication Board

The CS1W-SCB41-V1 installs on the CPU's option-board slot and exposes two serial ports. The mapping is fixed by hardware; you cannot change which port is RS-232 and which is RS-422/485.

4.1 DIP switch settings on the SCB41-V1

For the NT631C link on Port 2, set SW2 = OFF (RS-422 4-wire) and SW3 = ON only at the two physical ends of the multi-drop chain; never enable termination on the intermediate nodes or reflections will corrupt the 187.5 kbps signal.

4.2 PLC Setup words used by the SCB41

SCB41 port parameters live in the PLC Setup tree (CIO 162 / CIO 164 area), but the cleaner interface is the Serial Communication Unit / Board Setup dialog in CX-Programmer, which writes the correct combination of bits and baud-rate nibbles for you. Always validate with the SCB41 manual W336.

5. Programming the CPU - Peripheral Port vs. SCB41

The customer's SCB41-V1 is currently busy with the existing HMI. It is almost never a good idea to multiplex a programming session onto the same port that carries production traffic. The CS1G-CPU42 has a dedicated peripheral port on the front of the CPU, designed for the programming console and CX-Programmer. Use the Omron cable CS1W-CN114 (USB-to-peripheral) or the legacy CQM1-CIF02 (RS-232-to-peripheral).

1. In CX-Programmer choose PLC > Change PLC and set Network Type = Peripheral Bus.
2. Set the driver to SYSMAC CS/CJ Series Peripheral Port (USB) or Toolbus Auto-Detect at 115,200 bps.
3. Click Work Online. The CS1G will respond with its node address (default 00) and firmware version (e.g. CS1G-CPU42 V2.00).
4. If the CPU is in Run mode, CX-Programmer will request a privilege change; either accept the read-only monitor session or schedule a stop window.

Auto-detect removes the headache of guessing baud rate. Stick to Peripheral Bus rather than Toolbus on SCB41 Port 1; the latter forces the customer's HMI off the bus for the duration of the engineering session.

6. DeviceNet Network and DRM21-V1 Configuration

6.1 Master module and scan-list concept

The DRM21-V1 is a Master (Scanner) card. It holds a scan list - the polling table that maps each slave's input/output assembly to fixed CIO words on the CS1. With three DRT1-COM slaves total (one existing + two new), the scan list will contain three entries, each typically 4 words input + 4 words output for the standard Discrete I/O connection (COS disabled, polled, message group 2 only).

6.2 Two network-configuration modes

For a homogeneous DRT1-COM system, Fixed Configuration is the most reliable first step. Set the rotary switches on the DRM21 to Node 0, Baud = 500 kbps (the CS1G system default), and Mode = Fixed. On power-up, the master will discover any DRT1 slaves on the trunk and allocate them in order.

6.3 Uploading the existing DeviceNet project

1. Connect the PC to the CPU peripheral port (or to the SCB41 Port 1) with the Configurator's Online mode set to Network = DeviceNet > Serial Routing.
2. Right-click the DRM21 in the Configurator tree and select Upload from DeviceNet Master.
3. The Configurator will request the scan list and EDS parameter set; the upload typically takes 3-10 seconds per slave.
4. Save the project as CustomerPlant.cdm immediately. This file replaces the missing configuration the customer lost.

7. Troubleshooting DeviceNet Upload Errors

On the integrator's first attempt, two distinct errors were reported depending on the driver used.

7.1 Verification sequence after fixing the routing

1. Within the Configurator, go Online > Status > Master and confirm the DRM21 reports Online, Scan Mode = Run.
2. Expand the scan-list nodes. Each DRT1-COM should show Status = Online, Connection = Established.
3. From Edit > I/O Allocation Table, copy the CIO addresses into the CX-Programmer Symbol table (e.g. WordIn0 -> CIO 3300, WordOut0 -> CIO 3200). Save the symbol table as DevicenetMap.sym.

8. PID Loop Implementation in CX-Programmer

The CS1G-CPU42 supports the classic (194) PID instruction. The 194 instruction writes its working registers to a contiguous 33-word block beginning at the user-supplied base word. The structure is documented in detail in the CS/CJ Series Instructions Reference Manual (W340 / W474) which is part of the Digital Technical Library.

8.1 Ladder example - two PID loops

 |                                                |
 |   W0.00  (RunLoop1)                             |
 |------- | | ----------------------------( PID(194) D1000 )---
 |                                                |
 |   W0.01  (RunLoop2)                             |
 |------- | | ----------------------------( PID(194) D1100 )---

For loop 1, base = D1000; SP comes from D1000, PV from D1001, output is read at D1016 and routed to analog output. For loop 2, base = D1100. Always set Control Period in B+5 to be at least 3-5x the PV filter time and at least 1 s longer than the longest I/O scan.

8.2 Auto-tuning caveat

The CS1G-CPU42 implements the original 'limit-cycle' AT (auto-tuning) in the PID instruction. AT needs a stable process and will briefly bump the MV by 20-30 %. Confirm with the customer that the controlled actuator is rated for that transient before triggering AT in production.

9. NT631C HMI - NTLink 1:N Connection

The customer's NT631C supports NT Link 1:N. This allows up to 8 NS/NT series terminals to share a single RS-422 port on the SCB41.

1. On the SCB41 Port 2, set the protocol to NT Link 1:N with Highest Unit Number = 7.
2. On the NT631C, set the DIP switches for the desired PT number (1-7) and baud to 187.5 kbps (NT Link 1:N default).
3. Wire the RS-422 lines SDA / SDB / RDA / RDB with terminating resistors only at the two physical ends of the bus.
4. Allocate the area used by the HMI in CX-Programmer (e.g. PT1 = CIO 1500..CIO 1524, PT2 = CIO 1525..CIO 1549) and configure the same ranges in the NT631C project.

10. Optional Expansion - Adding CS1W-SCU21 or CS1W-SCU41

If the SCB41's two ports become saturated (one is now tied to NTLink, the spare is reserved for the integrators), a CS1W serial communication unit (not a board) can be added in a free CPU-rack slot. Both modules occupy one slot, take 20 CIO words for Software Switches / Status, and 100 DM words for setup.

For this project, an SCU21 would be the lowest-cost addition if the integrator wants a permanent engineering port (Toolbus on Port 1) independent of the SCB41.

11. Commissioning Checklist

1. Verify CS1G-CPU42 firmware version. CPU Menu > CPU Information shows CS1G-CPU42 Vx.xx. Printscreen to a PDF.
2. Upload the existing program, memory data, and DeviceNet configuration into a backup folder named YYYY-MM-DD_Backup.
3. Capture a Configurator diagnostic report (File > Save Diagnostic Report).
4. Open the new DeviceNet project, add the two new DRT1-COM nodes, and download the new scan list to the DRM21.
5. Power-cycle the DeviceNet trunk and confirm all three DRT1-COM slaves come online with green MS/NS LEDs.
6. From CX-Programmer, monitor the assigned CIO words and verify inputs toggle with sensor action.
7. Force a sample output word from CX-Programmer (right-click > Set > On) and confirm the field device responds.
8. Add the two PID blocks per Section 8, run an open-loop test, then enable AT only with the customer present.
9. Schedule the production cutover. Switch to Program mode, download, and observe for 15 minutes before releasing the line.

12. Field-Validated Caveats

• CS1G-CPU42 has no symbol memory. Any upload returns ladder + comments but no tag names. Recreate the symbol table from the customer's P&ID and wire it to the live I/O addresses.
• Battery maintenance. The CS1G uses a CJ1W-BAT01 lithium battery. The customer is running 24/7, so the battery has probably been replaced. The PLC Setup bit Battery Low is A402.04; alarm on this in the HMI.
• Fixed Configuration vs. Configurator. Switching the DRM21 between modes erases the scan list. Pick one mode and stay there.
• SCB41-V1 port numbering. Port 1 in the CX-Programmer dialog is the upper D-sub, Port 2 is the lower terminal block. Get this right the first time or you will spend a day chasing the wrong connector.
• Toolbus auto-detect. Use it. It is a 1-2 s connection at 115,200 bps, the fastest available on the CS1G peripheral port.

13. Related Manual and Resource Pointers

• CS1G-CPU42 Operation Manual (W339)
• CS/CJ Series Instructions Reference Manual (W340 / W474)
• DeviceNet DRM21-V1 Operation Manual
• CS1W-SCB41-V1 Serial Communication Board Operation Manual (W336)
• CX-One Integrated Tool Package product page
• Digital Technical Library request (through Omron rep)