Observed stale-response sequence
The GPIB-232CV-A is operating in C mode between a GPIB-connected computer and a serial-connected computer. The serial computer terminates each response with an EOS character—either carriage return or linefeed—and the GPIB application terminates reads on that EOS.
- The GPIB computer sends a query but does not read its response.
- The serial computer returns a response, which remains queued somewhere in the converter or host communication path.
- The GPIB computer sends a second query and performs a read.
- That read returns the first query's queued response rather than the second response.
What the evidence establishes
| Item | Engineering conclusion |
|---|---|
| EOS handling | Message termination works when the serial response ends with the configured carriage return or linefeed. |
| Unread response | Skipping a read leaves the corresponding response available to a later read. |
| Queue location | Unknown. The available behavior does not distinguish the converter buffer from a host-side GPIB or driver buffer. |
| Programmatic clear command | No supported command or API is identified in the evidence. |
| Serial-side read detection | No notification mechanism is identified that tells the serial computer whether the GPIB computer completed a read. |
Prevent response misalignment
Keep the transaction sequence deterministic: issue a query only when the application will consume its response. Pair every query with exactly one EOS-terminated read before issuing another query.
send(query)
response = read_until(configured_EOS)
associate(response, query)
If the application intentionally sends a query without using its result, still perform the corresponding read and discard that response before sending the next query. Do not assume that clearing only a local host buffer removes data already queued elsewhere in the path; the evidence does not identify where the unread response resides.
Verify synchronization
Send two queries with distinguishable expected responses. Read immediately after each query and confirm that each response matches the query that preceded it. Then repeat the original skipped-read sequence: if the next read returns the first response, the queue remains ordered and the application must drain or consume each transaction before proceeding.
FAQ
Why does the GPIB read return the previous query response?
The earlier query generated a serial response that was never read. That response remains queued and becomes the next data returned to the GPIB application.
Can I clear the GPIB-232CV-A buffer programmatically?
The supplied evidence identifies no supported buffer-clear command. Until the applicable command reference confirms one, consume and discard the unread EOS-terminated response before issuing another query.
Can the serial computer detect that the GPIB computer performed a read?
No such notification mechanism is established by the evidence. Design the exchange so every query receives one read, rather than making serial response generation depend on detecting a remote GPIB read.