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Supported SCPI status model

This framework implements a deliberately small, tested subset of IEEE 488.2 and SCPI status behavior:

operation/questionable condition
    -> positive transition event latch
    -> enable mask
    -> status-byte summary bit
    -> service-request enable mask
    -> MSS/RQS bit

standard event latch -> event-status enable -> ESB summary --+
error queue -------------------------------> error summary --+-> SRE -> MSS/RQS

Registers and bits

  • Operation and questionable condition registers are 15-bit values. A zero-to-one transition latches the corresponding event bit. Negative-transition filters are not implemented.
  • Reading an operation or questionable event register returns and clears that latch. The condition register is unchanged.
  • The Standard Event Status Register is an 8-bit latch. *ESR? returns and clears it. *ESE selects which latched bits assert ESB, status-byte bit 5.
  • A non-empty error queue asserts status-byte bit 2. Questionable and operation summaries use bits 3 and 7 respectively.
  • *SRE selects status-byte sources into bit 6, MSS/RQS. Bit 6 is a derived result, so writes to SRE bit 6 are ignored and *SRE? reports it cleared.
  • Every event read, enable write, error-queue change, *CLS, and STATus:PRESet recomputes summary and service-request state.

Common-command behavior

  • *CLS clears the error queue and all event latches. It preserves condition registers and enable masks and does not manufacture transition events.
  • STATus:PRESet clears operation/questionable event latches and their enable masks. It preserves condition registers, standard-event state, ESE/SRE, errors, and application tasks.
  • *RST awaits cancellation and cleanup of non-system application tasks, resets operation/questionable conditions, and performs *CLS.
  • *OPC waits for earlier application tasks and then latches Standard Event bit 0. *OPC? waits and returns 1 without changing that latch.
  • The self-test common command is implemented as the query *TST?.

This is not a claim of complete IEEE 488.2 or SCPI-1999 conformance. In particular, positive/negative transition filter commands, output-queue/MAV behavior, and a physical service-request line are outside the implemented subset.