The C200HS21 clock is reachable because Auto Online can read and adjust it. The failure is therefore in the connection context used by Work Online or by the custom program, not a blanket loss of clock function. Reproduce the working session, compare its communications path with the failing session, and test the USB-to-serial converter separately only after recording that baseline.
What do the symptoms isolate?
Read the sequence before changing settings. Successful clock access after Auto Online proves that Omron Programmer 3.0, the PLC clock, and at least one configuration of the serial path can complete the required exchange. A failure from the Project Workspace after Work Online shows that going online with the PLC does not necessarily create the same clock-access context.
The reported communications activity between the host and PLC confirms that bytes are moving, but it does not confirm that the request uses the right destination, session state, or command format. The longer delay before the error points to a request that waits for a valid response and then times out. Record the delay rather than treating activity indicators as proof of a valid transaction.
| Signal | Source | Wrong-value symptom |
|---|---|---|
| Online method | Omron Programmer 3.0 session |
Auto Online succeeds while Work Online reaches the PLC but clock access fails |
| PC communications port | USB-to-serial converter and operating-system assignment | Selecting COM3 when the working instance is on COM4, or the reverse, sends the request through the wrong interface |
| PLC endpoint | Processor comm2 connection |
A session aimed at another endpoint can appear online yet fail when a separate clock service is requested |
| Response timing | Request and PLC reply sequence | A delayed failure indicates that no acceptable clock response arrived before the software stopped waiting |
| Clock readback | PLC clock response | No returned value, an unchanged value, or an access error means the complete read or write transaction did not finish |
Why can Auto Online work when Work Online fails?
A clock operation has a signal chain: the software creates a clock request, the selected PC port transports it, the configured PLC endpoint receives it, and the PLC returns a response that the software must recognize. A break at any layer produces the same user-facing result: failed clock access.
Auto Online discovers or selects a usable communications context before opening PLC services. Work Online can use saved project settings instead. If that saved context differs from the discovered context, ordinary online monitoring may work while the separate clock request fails. The important comparison is not merely “online versus offline”; it is the port, endpoint, and session produced by each connection path.
A USB-to-serial converter adds another mapping layer. Seeing both COM3 and COM4 makes the selected operating-system port part of the diagnosis. Because other operations work, do not condemn the converter first. Confirm whether the successful and failing sessions address the same converter instance and PLC endpoint.
The phrase “program I've written” also creates two distinct cases. If the built-in Project Workspace clock function fails after Work Online, resolve that session mismatch before debugging application code. If only a separate program fails, compare its command, destination, port ownership, and response handling with the working built-in operation.
How do you reproduce the working connection?
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Create a baseline. Start Omron Programmer 3.0, use
Auto Online, open the clock, read it, and record the PC port, selected PLC endpoint, and connection choices displayed by the software. - Confirm a complete transaction. Read the clock twice. If an adjustment is operationally acceptable, make a small controlled correction and read the value back. A dialog opening without a returned value is not a successful test.
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Release the port. Close the clock view and end the online session cleanly. Close any other application that could hold
COM3orCOM4; two programs cannot reliably share one serial interface unless the driver explicitly provides that function. -
Rebuild the manual session. Use
Work Onlinewith the same PC port and the same processorcomm2endpoint recorded from the successful baseline. Do not change the cable, converter, PLC connection, and project settings in the same trial. - Test clock access immediately. Open the Project Workspace clock function before performing unrelated online operations. Record whether the failure is immediate or delayed and compare that interval with the baseline.
- Test the physical serial port as one controlled substitution. If a regular port is available, replace only the USB-to-serial path and repeat the same manual-session test. Success isolates the converter, its driver, or its port assignment; continued failure keeps the manual connection context and software path under investigation.
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Separate custom-code testing. After the built-in clock function works through
Work Online, run the written program with the same port and endpoint. Log the transmitted request, received bytes, and elapsed time to distinguish no response from a response the program rejects.
How do you verify that the fault is removed?
Use a small test matrix rather than one successful attempt. Run clock access after Auto Online, then after Work Online, and repeat both after restarting the software. The fix is verified when both paths return a clock value through the intended port without depending on a previous auto-online session.
For a write test, capture the value before adjustment, apply the approved correction, and read it back through a newly opened clock view. Then disconnect and reconnect once more. This checks the write response, persistent clock value, and fresh-session initialization separately.
If the direct serial port works but the USB converter does not, repeat the converter test using its confirmed operating-system port assignment. If COM3 and COM4 correspond to different instances or interfaces, label the working one and configure every access path to use it. A flashing activity indicator alone is not a pass criterion.
Which recurring pitfalls hide the root cause?
Changing several variables at once destroys the comparison. Hold the PLC endpoint, project, cable, and test action constant while changing only the online method or PC interface. Record the result of every trial.
Do not treat general PLC access as proof that every software service uses the same initialized session. The clock view may issue a separate request after the main online connection has been established. Likewise, do not tune application timeouts to hide a routing or session error; a longer wait cannot turn an invalid request into a valid response.
Port-name assumptions are especially unreliable with converters. Confirm the current assignment before each test and check that no terminal, programming package, or custom application already owns that port. When custom code is involved, test the built-in clock function first; debugging both the communications session and an unknown command implementation at the same time obscures the fault boundary.
FAQ
How do I fix C200HS clock access after Work Online?
Connect with Auto Online, record the working PC port and processor comm2 endpoint, then recreate those choices under Work Online. Restart the software and verify that the Project Workspace clock can read a value without a preceding auto-online session.
How do I test whether the USB-to-serial converter causes the clock error?
Repeat the same clock test through a regular serial port while keeping the project, PLC endpoint, and online method unchanged. If the regular port works, verify whether the converter is currently assigned to COM3 or COM4 and whether another application owns it.
When should I contact Omron support about C200HS clock access?
Stop after both Auto Online and a matched Work Online session have been tested through the converter and a regular port, with the failure timing recorded. Escalate if the built-in clock function still fails in a fresh session or if only the custom command fails despite a working built-in test. Give official Omron support the C200HS21 model, Omron Programmer 3.0 version, processor comm2 endpoint, PC port assignment, connection sequence, and exact displayed error text.