Help wanted: Voltcraft VC-890 protocol verification (real hardware needed)

[antoinecellerier]

Summary

The Voltcraft VC-890 protocol has been implemented based on clean-room reverse engineering of the Voltsoft DMSShare.dll software (same source as VC-880, but separate VC890Obj/VC890Reading classes), and has never been tested against real hardware.

The VC-890 is a 60,000-count OLED handheld DMM with a different protocol from the VC-880 — polled (request/response) instead of streaming, 66-byte frames instead of 39, remapped function codes, and 60K count ranges.

What we need

Someone with a Voltcraft VC-890 multimeter and the CP2110 USB adapter.

What needs verification

• Polled communication model — does sending 0x5E produce a measurement response?
• Frame extraction (66-byte, AB CD header, BE16 checksum)
• Function code mapping (19 codes, 0x00-0x12, remapped from VC-880):
  • 0x00=ACV (not DCV!), 0x02=DCV, 0x03=AC+DC V, etc.
• 60,000 count range values (6V/60V/600V vs VC-880's 4V/40V/400V)
• Main display value (7 ASCII bytes) — parsed values match OLED?
• 6 additional sub-display fields — format and content
• Status flag bytes (8 bytes at msg[56..63]):
  • Byte 57: Rel(0), Avg(1), Min(2), Max(3)
  • Byte 58: Hold(0), Manual(1), OL1(2), OL2(3)
  • Byte 59: AutoPower(0), Warning(1), Loz(2), Void(3)
• Battery level nibble (msg[62]) — what do the values mean?
• Misplug warning nibble (msg[63]) — 0=none, 1=mA err, 2=A err?
• Ack protocol (0xFF+[0x00] after responses) — is it required?
• Commands: hold, rel, range_auto/manual, max_min_avg, light, select
• PC button activation requirement

Verification steps

1. Enable USB communication

Press the PC button on the meter.

2. Run the capture wizard

cargo run --bin dmm-cli -- --device vc890 capture

3. Raw byte dump

RUST_LOG=dmm_lib=trace cargo run --bin dmm-cli -- --device vc890 debug

4. Basic reading

cargo run --bin dmm-cli -- --device vc890 read --count 10

What to report

• Meter model and firmware version if known
• OS and version
• Result of each step
• LCD/OLED screenshots alongside tool output are very helpful

Protocol reference

See docs/research/vc890/reverse-engineered-protocol.md for the wire protocol specification.

[antoinecellerier]

Protocol-correctness review update (2026-06)

Re-audited the VC-890 parser against the Voltsoft DMSShare.dll decompile (VC890Obj/VC890Reading). Two fixes, both decompile-derived (no VC-890 hardware available).

Fixed (corrected from vendor, hardware confirmation pending)

• ACV LPF (function 0x01) range — the vendor never reads the range byte for LPF and fixes the range at 1000V (case 1, DMSShare_decompiled.cs:23466-23469); we previously indexed the shared voltage table with an undefined byte. What does the meter actually send in the range byte for LPF?
• Misplug nibble — the warning nibble has a fourth value: 3 = "ERROR ON V INPUT" (23649-23665), in addition to 0/1(mA)/2(A).

Newly logged open questions

• Inbound checksum — the vendor never validates meter→host checksums; our BE16 check is inferred from the host-side builder. If real frames are all rejected with ChecksumMismatch, suspect a different inbound scheme.
• Command confirmation frames — the vendor's SendCommand waits for a frame whose type byte equals the command byte (5 retries); we fire-and-forget.

Plus the existing open items (ack-protocol necessity, battery nibble scale). Capture with cargo run --bin dmm-cli -- --device vc890 capture.