Omron C200HS Program Download: Preserving DM and HR Memory Areas

The Omron C200HS CPU distinguishes between the user program (ladder logic stored in the UM/Program Memory region) and the data memory regions (D, H, IR, SR, AR, LR, TC, EM). A program download through CX-Programmer targets the Program Memory area only and does not overwrite data memory values, provided the CPU retains its backup battery and the PLC is in the correct operating mode. This technical reference documents the exact behavior of each memory area during a program transfer, the proper backup procedure for the .mem file, DIP switch configuration for Memory Cassettes, and verification steps using CX-Programmer 7.2 / CX-One 4.x.

C200HS Memory Architecture Overview

The C200HS CPU organizes its address space into several discrete regions, each with its own retention characteristics and access rules. The official C200HS Operation Manual (W235-E1-05) defines the complete map and the boundaries between program and data storage. The regions relevant to a routine program download are summarized below.

The C200HS CPU uses a memory architecture in which the ladder program occupies the UM (User Memory) region while data regions such as DM (D), HR (H), IR, LR, TC PV, and EM are mapped into a separate SRAM area protected by the lithium backup battery. Because of this physical separation, the standard CX-Programmer Transfer to PLC → Programs command writes only the UM region. The data regions remain untouched.

What CX-Programmer Actually Transfers on a Program Download

When CX-Programmer performs a Transfer to PLC operation with Programs selected, it sends the ladder diagram, expansion instructions, and task structure to the C200HS Program Memory area. The Host Link protocol (C-mode or FINS) handles this as a discrete write to the program area.

According to the operation manual, the program area is independent of the data memory area, and the host link command set includes dedicated function codes for each:

Because each region uses a separate command code, the standard program transfer (WR/WG) cannot accidentally overwrite DM, HR, AR, LR, IR, or EM. The KEPServerEX driver documentation for the Omron Host Link driver confirms the same partitioning: C200H Addressing defines DM, HR, AR, IR, and LR as independent I/O tags that are read and written through dedicated channels, never bundled into the program memory image.

Memory Areas Surviving a Standard Program Download

For a typical CX-Programmer transfer to a powered C200HS with healthy battery voltage, the following data regions retain their values intact:

1. DM (Data Memory, D0000–D6655) — All 6,656 words remain unchanged. CX-Programmer treats DM as a separate "memory component" and requires an explicit Transfer operation.
2. HR (Holding Relay, H000–H9915 / HR00–HR99) — All 1,600 retentive bits retain state. The HR area is preserved across power cycles and across program downloads.
3. AR (Auxiliary Relay) — System diagnostic flags retain their values; flags driven by firmware may refresh at next scan.
4. LR (Link Relay) — All 1,024 link relay bits remain intact.
5. TC PV (Timer/Counter Present Values) — Retentive timers and counters (designated by retention attribute in the program) keep their PV. Non-retentive timers reset to SV on the next scan cycle.
6. EM (Extended Memory) — When present, EM banks retain contents unless the EM bank itself is being re-initialized by the new program.
7. IR/SR — I/O bits refresh on next I/O refresh; special relays are recomputed by firmware.

Pre-Download Backup Procedure

Although a routine program download is non-destructive, the C200HS has several operations that do erase data, and any of these can be triggered accidentally from the CX-Programmer menu or by a Memory Cassette mount operation. Back up the program and all data areas as separate files before every download.

Prerequisites

• CX-Programmer 7.2 or later (the recommended upgrade path from version 3.0). CX-One 4.x or later bundles CX-Programmer with the Sysmac Studio back-compatibility components.
• C-series (C200HS) Host Link cable, USB-Serial adapter approved by Omron, or the later CP1W-CIF01 / CS1W-CN226 over Ethernet (with FINS gateway).
• CPU in PROGRAM mode if any HR/TC/LR/EM transfer is required. The D area can be transferred in RUN or MONITOR mode.
• A known-good lithium backup battery (CR14250SE or equivalent) with voltage ≥ 2.8 VDC. Low-battery detection (AR0804 = ON) must be clear before backup.

Step-by-Step Backup in CX-Programmer

1. Connect CX-Programmer to the C200HS via Host Link (default settings: 9,600 baud, unit number 00, C-mode protocol).
2. Place the PLC in PROGRAM mode using the mode switch on the CPU faceplate or via PLC → Operating Mode → Program in CX-Programmer.
3. Right-click the PLC node and choose Transfer From PLC → Programs. Save the resulting file as project_backup.cxp.
4. Open Memory Component from the project tree. This is the "Memory" view that displays D, H, W, A, T/C, and EM areas as discrete data tables.
5. Open the D area tab. Select the full range (D0000–D6655). Right-click and choose Transfer From PLC → D. Save the file with extension .mem (e.g., D_area_backup.mem).
6. Open the H area tab. Select HR00–HR99. Right-click and choose Transfer From PLC → H. Save the H-area contents to a separate .mem file. Note that transferring the H area requires the CPU to be in PROGRAM mode.
7. Repeat for the A (AR) area, W (LR) area, T/C PV area, and any EM banks present. Each region produces its own .mem file.
8. Close all open transfers. Verify file sizes: a full D-area .mem file for the C200HS is approximately 16 KB (D0000–D6655 = 6,656 words × 2 bytes + CX-Programmer header). A full H-area .mem file is approximately 200 bytes (HR00–HR99 = 100 words).
9. Archive the program file and all .mem files into a project-named folder. Label the folder with the date, CPU serial number, and program revision.

Performing the Program Download

With backups verified, the program transfer proceeds normally.

1. Open the new project file in CX-Programmer 7.2 (or the version used to author the program).
2. Confirm the target PLC type in the project properties: Device Type = C200HS and CPU model match (e.g., CPU21, CPU23, CPU31).
3. Go online: PLC → Work Online (or Ctrl+W). Verify the connection reports the correct CPU model.
4. Select PLC → Transfer → To PLC. The Transfer to PLC dialog appears with check boxes for Programs, Memory, Expansion Instructions, and I/O Comments.
5. Select Programs only. Deselect Memory, Expansion Instructions (unless intentionally upgrading), and I/O Comments. Click OK.
6. CX-Programmer prompts: "The CPU will be placed in PROGRAM mode. Continue?" Click Yes.
7. The transfer writes the program memory. A progress bar shows the percentage completion. Typical transfer time for a 16 K-step C200HS program over 9,600 baud Host Link is 30–90 seconds.
8. When transfer completes, the PLC remains in PROGRAM mode. Switch back to MONITOR or RUN using the mode switch to begin execution.

Restoring Data Memory After Download

If for any reason the D or H area values are cleared during the procedure (typically due to an explicit Memory Component transfer, a clear-all operation, or a battery-failure-induced reset), restore from the saved .mem files.

1. Ensure CPU is in PROGRAM mode. The H area (and most AR/LR areas) require PROGRAM mode for write access via Host Link.
2. Open the Memory Component view and select the D area tab.
3. Right-click and choose Transfer To PLC → D. Navigate to D_area_backup.mem and confirm.
4. Repeat for the H area: Transfer To PLC → H with H_area_backup.mem.
5. Repeat for A, W, T/C, and EM banks as needed.
6. Verify each restored area by spot-checking values against the original archive.
7. Switch to MONITOR/RUN mode.

DIP Switch and Memory Cassette Considerations

When the program is stored on an EPROM Memory Cassette (e.g., C200HS-ME16K), the DIP switch on the CPU faceplate controls whether the cassette is read-only or read/write, and whether the program is loaded from the cassette to internal RAM at power-up.

If the new program is stored on a Memory Cassette, mount the cassette on the CPU, set the DIP switches appropriately, and power-cycle to load the new program. The auto-load operation writes the program area only — DM, HR, and EM values in internal SRAM remain intact as long as the battery holds voltage during the power cycle.

CX-Programmer Version Compatibility

CX-Programmer 3.0 (released with the original C-series support package) communicates correctly with the C200HS using the standard C-mode Host Link protocol, but lacks support for later C200HS firmware features, the FINS communications protocol, and the structured text editor improvements. The recommended upgrade is CX-Programmer 7.2 (the last version with full C200HS support as a primary target) bundled within CX-One 4.x.

Newer CX-Programmer versions (9.x and later) maintain backward compatibility with C200HS project files, although some advanced features may be silently ignored when uploaded from the older PLC. The .cxp project file format has remained compatible across these versions for the C200HS device type.

Memory area file extension handling:

• .cxp — full CX-Programmer project including ladder, I/O comments, and Memory Component data tables
• .mem — Memory Component transfer file (D, H, A, W, T/C, EM, or combined)
• .exp — Expansion Instructions file (function block libraries)
• .txt or .csv — human-readable export of Memory Component tables

Verification Procedure After Download

After the program download and any required data restore, validate the system before returning to production.

1. Verify CPU mode is set to the intended operating state (RUN or MONITOR).
2. Check error indicators: AR0800 (cycle time over), AR0801 (I/O verify error), AR0804 (battery error). All should be OFF.
3. Read back a sample of D, H, A, and W areas using the Memory Component view. Confirm the values match the pre-download backup.
4. Spot-check any retentive timers (TCxxx with retentive attribute): the PV should equal its pre-download value.
5. Force a single scan in MONITOR mode by toggling the AR0900 step flag. Observe the program execution for any faults.
6. Monitor the cycle time in SR237/SR238 (scan time high/low words). A significant change from baseline indicates the new program has different scan behavior.
7. Verify I/O: scan IR000–IR015 input words and confirm field devices register correctly. Verify output words IR100–IR115 drive the expected loads.

Troubleshooting Matrix

Field-Engineer Checklist for Safe Program Updates

1. Confirm CPU type, model, and firmware revision match the target project.
2. Check battery voltage (AR0804 OFF) and record the date.
3. Upload the existing program and all data area .mem files. Save with timestamped filenames.
4. Compute checksum or spot-check a few critical D/H values; record them on the work order.
5. Place the PLC in PROGRAM mode.
6. Transfer the new program only (not Memory, not Expansion Instructions, unless intentional).
7. Verify program transfer completed without errors.
8. Restore any data memory that the new program explicitly requires, if data map changed.
9. Switch to MONITOR mode and perform a controlled test scan.
10. Switch to RUN mode for production. Archive all backup files with the work order.

Related Omron C-Series Documentation

For engineers maintaining C200HS systems alongside newer CP1E, CP1L, or CJ2 CPUs, note that the same memory partition philosophy applies. The DM, HR, AR, LR, and EM regions exist in all C-series PLCs and are always preserved across standard program downloads. The CX-Programmer Memory Component interface exposes identical backup and restore operations for all of these platforms.

The complete C200HS operation procedures, error codes, and DIP switch definitions are documented in the official C200HS Operation Manual (W235-E1-05). Host Link addressing conventions and the C200H memory model are summarized in the KEPServerEX driver documentation: C200H Addressing in Omron Host Link Driver.