S Groesz
a5ee5781de
Complete extraction of all 97 commands in HP 3457A Operating.pdf Chapter 4, expanded to 120 JSON entries (F10-F58 modeled as 24 independent commands rather than one parameterized command). Each entry includes description, syntax, structured parameters, important points, worked examples, and tier/rationale classification to guide which commands a Python control library actually needs. Documents several findings not obvious from the manual alone: the output buffer's single-reading data-loss behavior and the correct burst-acquisition pattern, the CR/LF bus-hold gotcha, the Front Panel checkbox's unreliability, the isolation-link mechanism behind F10-F58's speed, and memory/timing capacity math for burst captures. Updates README.md (was empty) and cmdformat.txt to document the schema and key findings.
128 lines
7.1 KiB
Markdown
128 lines
7.1 KiB
Markdown
# HP 3457A
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Reverse-engineered GPIB command reference for the HP 3457A digital
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multimeter, built toward a Python control library. The instrument
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predates SCPI/IEEE-488.2, so it doesn't understand `*IDN?` and friends —
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it has its own compact command language, documented only in the PDF
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manuals below.
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## Contents
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- **`commands.json`** — the deliverable. A complete, hand-verified,
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structured extraction of every command in Chapter 4 ("Command
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Reference") of `HP 3457A Operating.pdf`: 97 documented commands,
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expanded to 120 JSON entries (the `F10`–`F58` family is 24 independent
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zero-parameter commands crammed onto one manual page — modeled here as
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24 separate entries, not one command with 24 parameter choices). Each
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entry has description, syntax, structured parameters (typed value
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tables with power-on/default flags where the manual provides them),
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important points, and worked examples, plus two classification fields
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not in the manual (see below). Read the `_meta` block at the top of the
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file first — it documents the schema and a dozen cross-cutting findings
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that took real digging to establish, not just page-by-page
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transcription.
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- **`cmdformat.txt`** — the schema outline `commands.json` follows.
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- **`HP 3457A Operating.pdf`** — the real command/operating reference.
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Chapter 4 is the source for `commands.json`; Chapter 1 has the
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abbreviated specifications (accuracy, reading rates, memory); Chapter 3
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has the conceptual explanations (triggering, math operations, buffers)
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Chapter 4 assumes you've already read.
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- **`HP 3457A Service.pdf`** — board-level theory of operation and
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schematics. Poor OCR/scan quality throughout (don't expect a clean
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full-text read), but worth a targeted search when a specific mechanism
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needs explaining — e.g. it's what revealed the opto-isolated
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master/slave-processor link that explains why `F10`–`F58` execute
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faster than `DCV`/`OHM`/`OHMF`.
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- **`GPIBProgrammingReferenceManual.pdf`** — despite the filename, this is
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a *generic* Advantech GPIB interface-card primer (bus concepts,
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IEEE-488 basics), not HP 3457A-specific. Useful for general GPIB
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background, not command syntax.
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## `commands.json` at a glance
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Every entry carries two classification fields beyond what the manual
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documents, meant to guide what a Python library should actually expose:
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- **`tier`** — does a typical automated measurement workflow need this?
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`core` (40 — measurement functions plus the setup/trigger/timing/status
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commands a controller genuinely can't replicate host-side), `protocol`
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(3 — `ADDRESS`/`END`/`INBUF`, bus/transport housekeeping), `extended`
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(77 — real and documented, but not needed for typical use: plug-in-card
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commands, on-instrument program/state storage a host script replaces,
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calibration/diagnostics/service, front-panel UI, legacy speed-optimized
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aliases).
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- **`rationale`** — *why* does this exist / why is it fast? Distinguishes
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genuine hardware advantages that remain relevant today
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(`measurement_hardware`, `acquisition_timing`) from things that only
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mattered because 1980s host controllers were slow or limited
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(`era_computer_workaround`), plus a few narrower buckets
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(`wire_efficiency`, `plugin_card_dependent`, `diagnostic_calibration`,
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`status_error_readback`, `ui_frontpanel_only`, `bus_protocol`).
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`tier` and `rationale` are independent axes and are allowed to disagree —
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e.g. the `MEM` reading-memory family is `extended` tier (most workflows
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don't need it) but `acquisition_timing` rationale (genuinely valuable
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*if* burst throughput matters).
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### Notable findings baked into `_meta`
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- **Only `ADDRESS` is Remote-unchecked** across all 120 entries — you
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can't remotely reassign the instrument's own bus address. Everything
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else is fully GPIB-controllable. `POWER` isn't a documented command at
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all (pure physical switch).
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- **The Front Panel checkbox is unreliable** as a "what's physically
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possible" signal — `DCV`/`ACV`/`ACI`/`ACDCV`/`DCI` are all marked
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unchecked despite having real dedicated/shifted panel keys; `ACDCI` is
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checked despite Chapter 3 describing it in word-for-word parallel terms
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to its siblings (almost certainly a manual erratum on the `ACDCI` page).
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- **The output buffer holds exactly one reading** and silently overwrites
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it if not drained in time — there is no GPIB streaming mode. The
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documented high-throughput pattern is `NRDGS <count>` + a single
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`TRIG SGL`, which runs the whole burst to completion *inside* the
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instrument (bus held throughout) before you pay any transfer cost.
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`MATH STAT`/`PFAIL` are the two math operations that don't alter the
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reading, so they accumulate accurate aggregates across a burst even
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when individual readings never make it off the bus — genuinely useful
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for a burst that outruns the transfer channel, not a 1980s-era
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workaround.
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- **CR/LF bus-hold gotcha**: with the input buffer off (its power-on
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default), the instrument holds the HP-IB bus until a command finishes
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executing, because it processes `<CR>` immediately but not `<LF>` until
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done. Explains earlier confusing "dropped command" symptoms seen live
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on this project's hardware.
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- **Memory/timing math**: 2208 bytes total (reading/subprogram/state,
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via `MSIZE`); reading-memory format (`MFORMAT`) determines bytes/sample
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(2–16); the empirical reading-rate table tops out at 1350 readings/sec
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(`DCV`, 3.5 digits, autozero off) — filling the ~1053-sample max buffer
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at that rate takes ~0.78s. `ACV`/`ACI` cap out ~140x slower (~9.5
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rdg/s) since AC measurement is internally-aggregated, not instantaneous
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sampling — so `DCV` burst mode is the only realistic way to approximate
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an oscilloscope-style capture with this instrument.
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Full detail, sourcing, and page references for all of the above are in
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`commands.json`'s `_meta` block.
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## Related work reviewed
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- [sigrok's `hp-3457a` driver](https://github.com/sigrokproject/libsigrok/tree/master/src/hardware/hp-3457a) —
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thin coverage: measurement-mode selection, NPLC, terminal switching,
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autorange query, `RMATH HIRES`, rear-card scan-list plumbing. No
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`PER`, no explicit range/resolution, no `FSOURCE` (flagged `TODO` in
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their own code), nothing for math/calibration/display/subprograms.
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- [MikeDombo/HP3457A-GPIB](https://github.com/MikeDombo/HP3457A-GPIB) —
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a wxPython measurement GUI. Confirmed real-world use of the `F10`-`F58`
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shorthand family and the `TERM 1`/`TERM 2` numeric equivalents.
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## Status / next steps
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`commands.json` is complete and is the ground-truth spec for the planned
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Python control library, which hasn't been started yet. The transport
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layer (Prologix GPIB-ETHERNET controller) already exists in the sibling
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repo `progpib` — the plan is to build HP 3457A-specific command wrappers
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on top of that rather than reimplementing GPIB transport here. One
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documented gap remains: the separate "HP-IB Commands" section (manual
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pages 4-167–4-174, generic IEEE-488 bus messages like `CLEAR`/`LOCAL`/
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`REMOTE`) hasn't been extracted into `commands.json` yet, since it likely
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maps to functionality `progpib` already exposes at the transport layer
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rather than needing instrument-specific wrappers.
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