Siemens controls technical resource
S7-300 CPU 315-2 DP OB122 events: 16#2942 and 16#2943
A sanitized WES diagnostic-buffer record identifies an S7-300 CPU 315-2 DP and reports repeated I/O access errors: 16#2942 while reading and 16#2943 while writing, with OB122 named as the requested organization block. The record does not establish the initiating cause, the CPU's operating mode, whether OB122 executed successfully, any corrective work, or the machine's final state.
What the archived record actually says
The WES text export lists order number 6ES7315-2AG10-0AB0, hardware version 4 and firmware V2.0.11. Its event entries describe word accesses in the P area and request I/O access error OB (OB122). The addresses and project-specific details are intentionally omitted.
This is evidence of logged read/write access events—not a confirmed failed module, PROFIBUS station outage, CPU STOP, repair or successful restart.
Keep the recorded event separate from a diagnosis
Siemens describes OB122 as the S7-300/400 I/O access error organization block. The operating system calls it when an error occurs while accessing module data. That definition explains the diagnostic category; it does not identify which physical component or configuration condition caused a particular access to fail.
The cited Siemens reference covers S7-300/400 system functions; it is not a release note for firmware V2.0.11. No firmware-specific cause or corrective action is inferred here.
How 16#2942 and 16#2943 differ
In its OB122 start-information table, Siemens lists event class B#16#29 separately from the read/write error codes B#16#42 and B#16#43. The WES diagnostic buffer itself prints event IDs 16#2942 and 16#2943 and spells out the matching access directions.
WES event text and Siemens OB122 code meanings
The comparison table can be scrolled horizontally on a narrow screen.
| Recorded event ID | WES buffer wording | Siemens-defined distinction | Not established by this entry |
|---|---|---|---|
16#2942 |
I/O access error while reading; P-area word access is shown. | B#16#42 is an I/O access error, reading. |
The cause, physical module, address mapping, CPU mode and machine consequence. |
16#2943 |
I/O access error while writing; P-area word access is shown. | B#16#43 is an I/O access error, writing. |
That a module was missing or defective, that an output changed, or that the CPU stopped. |
Siemens documents the OB122 memory-area field as encoding access type and memory area separately, with another field for the address. The WES export's “P area, word access” wording describes the logged access context; it does not name a PROFIBUS node or prove a particular module failed. The exact project addresses are withheld from this public page.
Siemens: System Software for S7-300/400, System and Standard Functions, Volume 1/2 (Reference Manual, 05/2010, A5E02789976-01), section 1.28. Use the CPU-specific manual for version-dependent details.
Possible causes are investigation questions, not findings
Siemens' STEP 7 programming manual gives examples of OB122 access errors that include direct I/O access to a defective or missing module and access to an I/O address unknown to the CPU. Those are general examples from Siemens documentation—not conclusions about the WES record.
- Address/configuration question: Does the logged read or write address correspond to the intended configured I/O area in the matching, authorized STEP 7 project?
- Module-availability question: Do the existing hardware diagnostics and site records show the configured module was present and available at the time? The buffer excerpt alone does not answer this.
- Execution-context question: Which block and instruction were active, and what adjacent diagnostic entries identify the event sequence? Siemens notes that the OB122 block-type, block-number and relative-address fields are not valid for S7-300; do not assume this buffer will identify a usable source block or instruction.
A matching hypothesis is not a repair instruction. Do not replace a module, alter an address, download a program or change I/O behavior solely because one of these possibilities appears in a manual.
Siemens: Programming with STEP 7 V5.4 (Manual, 03/2006, A5E00706944-01), section 23.9.15, provides the general OB122 examples and an example using event IDs 16#2942/16#2943. Its example is not evidence of the cause in this separate record.
Safe evidence review
Operators can note only what is already visible and safe to observe: the HMI message, any CPU RUN/STOP indication visible without opening equipment, when the symptom was noticed, and whether the machine's visible state changed. Do not open an energized cabinet or reset equipment to collect a code.
For qualified, authorized controls personnel
- Preserve the existing diagnostic buffer and entries around the event before clearing or changing anything.
- Confirm the CPU order number and firmware from the installed system; compare them with the project copy and the Siemens documentation for that exact version.
- Using the authorized project, correlate each retained access address and read/write direction with the configured I/O map, the relevant instruction and available module diagnostics.
- Separate an explicit CPU mode-transition entry from an OB122 request. Siemens states that an unprogrammed OB122 can cause RUN-to-STOP; this WES excerpt does not establish whether that condition occurred.
Firmware and evidence limits
The WES record identifies CPU 315-2 DP order number 6ES7315-2AG10-0AB0 and firmware V2.0.11. A Siemens module list identifies the spaced order number 6ES7 315-2AG10-0AB0 as a CPU 315-2 DP with firmware V2.0; that supports the model and firmware branch, not a V2.0.11-specific diagnosis. The S7-300/400 system-functions reference supports interpretation of the read/write fields, but no exact-release cause or repair is inferred. Match the installed CPU and firmware to the applicable historical Siemens documentation before any engineering change.
Siemens: New Modules Supported from STEP 7 V5.1 SP4 Onwards (04/2002, A5E00140278-02), used here only to identify the CPU model/firmware branch.
The available log does not establish the actual RUN/STOP sequence, a particular I/O module or network fault, a root cause, corrective work, or whether the machine returned to service. No outcome is implied.