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PROTOCOL.md
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PROTOCOL.md
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# HPCS 6500 USB Protocol Reference
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Reverse-engineered from USB packet captures of the vendor software.
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## Device Overview
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The HPCS 6500 is a spectrophotometer / integrating sphere system for LED and
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light source testing. It includes a built-in programmable AC/DC power supply.
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**Capabilities:**
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- Spectral power distribution (380-1050 nm, 350 points)
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- Photometric values (lumen, luminous efficacy, CCT, CRI Ra/R1-R15)
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- Chromaticity coordinates (CIE xy, uv, u'v')
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- Radiometric flux (total, UV, blue, yellow, red, far-red, IR)
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- CIE 1931 tristimulus (X, Y, Z), TLCI-2012, SDCM
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- Electrical parameters (voltage, current, power, power factor, frequency)
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- Harmonics analysis (50 harmonics voltage/current %, UThd, AThd, waveforms)
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- Built-in power supply: AC 100-240 V / 50-60 Hz, DC 1-60 V / 0-5 A
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**Connection:**
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- USB interface via STM32 Virtual COM Port (VID `0483`, PID `5741`)
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- Appears as a serial port (e.g. COM42 on Windows)
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- Baud rate: 115200
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## Frame Format
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Every command and response starts with the sync byte `0x8C` followed by a
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command ID byte. The device echoes the command ID in the response. All
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multi-byte numeric values are **little-endian**.
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```
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TX: 8C <cmd> [payload...]
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RX: 8C <cmd> [data...]
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```
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Write commands receive a 2-byte ACK (`8C <cmd>`). Read commands return
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variable-length data after the 2-byte header.
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## Command Table
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| Cmd | Direction | TX len | RX len | Description |
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|------|-----------|--------|----------------|--------------------------------------|
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| `00` | read | 2 | 16 | Identify device |
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| `01` | write | 6 | 2 | Set integration time (uint32 LE, µs) |
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| `03` | read | 2 | 9 | Poll instrument state |
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| `05` | read | 2 | 7 | Status check |
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| `0E` | write | 3 | 2 | Start (`01`) / Stop (`02`) measuring |
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| `13` | read | 2 | 4 hdr + 3904 | Read measurement block |
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| `25` | write | 2 | 2 | Reset instrument |
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| `26` | read | 2 | 196 | Read instrument ranges |
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| `2A` | read | 2 | 122 | Read device configuration |
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| `72` | write | 3 | 2 | PSU output on (`00`) / off (`01`) |
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| `73` | write | 7 | 2 | Set DC parameter (sub + float32) |
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| `77` | read | 2 | 4 hdr + 1584 | Read electrical / harmonics block |
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| `78` | write | 7 | 2 | Set AC parameter (sub + float32) |
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| `79` | read | 2 | 20 | Read power supply settings |
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| `7A` | write | 3 | 2 | Set output mode (`00`=AC, `01`=DC) |
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| `7B` | read | 2 | 2 | Read output mode |
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## Measurement Sequence
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```
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1. TX 8C 00 -> Identify (expect "HPCS6500" in response)
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2. TX 8C 79 -> Read current PSU settings
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3. TX 8C 7A <mode> -> Set output mode (00=AC, 01=DC)
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4. TX 8C 78/73 ... -> Configure voltage/frequency/current as needed
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5. TX 8C 01 <uint32> -> Set integration time (µs), or skip for auto
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6. TX 8C 72 00 -> Turn PSU output ON
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7. TX 8C 0E 01 -> Start measurement
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8. TX 8C 03 -> Poll state until byte[2] = 0x01 (data ready)
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9. TX 8C 13 -> Read measurement data (3904 bytes)
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10. TX 8C 77 -> Read electrical data (1584 bytes)
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(repeat 8-10 for continuous readings, ~550 ms per cycle)
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11. TX 8C 0E 02 -> Stop measurement
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12. TX 8C 72 01 -> Turn PSU output OFF
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13. TX 8C 25 -> Reset instrument
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```
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## State Polling (`8C 03`)
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9-byte response: `8C 03 <b2> <b3> <b4> <b5> <b6> <b7> <b8>`
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| Byte | Meaning |
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|------|------------------------------------------------------|
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| b2 | Data flag: `00` = no new data, `01` = data available |
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| b3 | Mirrors b2 |
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| b4 | Always `00` |
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| b5 | State: `04` = idle, `01` = measuring |
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| b6 | Always `00` |
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| b7 | Always `00` |
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| b8 | Always `01` |
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## Measurement Block (`8C 13` — 3904 bytes)
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The response has a 4-byte transport header (`8C 13 0F 40`) followed by a
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3904-byte payload. All floats are IEEE 754 single-precision, little-endian.
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### Device Header (offset 0-35)
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| Offset | Size | Type | Field |
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|--------|------|--------|---------------------------|
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| 0 | 10 | ASCII | Device ID (`"HPCS6500"`) |
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| 10 | 26 | — | Internal calibration data |
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### Photometric (offset 36-75)
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| Offset | Type | Field | Unit | Example |
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|--------|---------|------------------------|---------|---------|
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| 36 | float32 | Luminous flux | lm | 479.57 |
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| 40 | float32 | Luminous efficacy | lm/W | 57.05 |
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| 44 | float32 | Correlated color temp | K | 5653 |
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| 48 | float32 | Duv | — | 0.00553 |
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| 52 | float32 | CIE x | — | 0.3289 |
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| 56 | float32 | CIE y | — | 0.3489 |
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| 60 | float32 | CIE u | — | 0.2015 |
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| 64 | float32 | CIE v | — | 0.3206 |
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| 68 | float32 | CIE u' | — | 0.2015 |
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| 72 | float32 | CIE v' | — | 0.4809 |
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### Color Rendering (offset 76-143)
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| Offset | Type | Field | Example |
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|--------|---------|-------|---------|
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| 76 | float32 | SDCM | 4.71 |
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| 80 | float32 | Ra | 83.0 |
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| 84-140 | float32 | R1-R15 (4 bytes each) | R1=82 .. R15=76 |
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R*n* is at offset `80 + n × 4` (R1 at 84, R2 at 88, ..., R15 at 140).
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### Radiometric (offset 144-175)
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| Offset | Type | Field | Unit | Example |
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|--------|---------|--------------------|------|----------|
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| 144 | float32 | Total radiant flux | mW | 1491.256 |
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| 148 | float32 | UV flux | mW | 0.000 |
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| 152 | float32 | Blue flux | mW | 469.836 |
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| 156 | float32 | Yellow flux | mW | 679.454 |
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| 160 | float32 | Red flux | mW | 330.864 |
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| 164 | float32 | Far-red flux | mW | 11.462 |
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| 168 | float32 | IR flux | mW | 0.000 |
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| 172 | float32 | Total (duplicate) | mW | 1491.256 |
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### CIE Tristimulus & Sensor (offset 224-255)
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| Offset | Type | Field | Example |
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|--------|---------|----------------|---------|
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| 224 | float32 | CIE 1931 X | 661.9 |
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| 228 | float32 | CIE 1931 Y | 702.15 |
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| 232 | float32 | CIE 1931 Z | 648.535 |
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| 236 | float32 | TLCI-2012 | 68 |
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| 244 | float32 | Peak Signal | 53088 |
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| 248 | float32 | Dark Signal | 2267 |
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| 252 | float32 | Compensate lvl | 2834 |
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### Timestamps (offset 272-291)
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| Offset | Size | Type | Field | Example |
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|--------|------|-------|-----------|----------------|
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| 272 | 11 | ASCII | Test date | `2026-02-04\0` |
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| 283 | 9 | ASCII | Test time | `16:04:17\0` |
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### Spectral Data (offset 432-1831)
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| Offset | Type | Field |
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|-----------|---------------|----------------------------------|
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| 430-431 | uint16 | Spectrum header (zero) |
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| 432-1831 | float32 × 350 | Spectral irradiance (µW/cm²/nm) |
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The 350 floats cover **380 nm to 1050 nm** at ~1.92 nm steps
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((1050-380) / (350-1) = 1.917 nm/step). Values are absolute spectral
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irradiance; the vendor software normalizes by dividing by the peak value.
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### Unmapped Regions
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Offsets 176-223, 256-271, and 1832-3903 contain additional data not yet
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fully mapped. They likely hold extended parameters visible in the vendor
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software's advanced views.
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## Electrical / Harmonics Block (`8C 77` — 1584 bytes)
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The response has a 4-byte transport header (`8C 77 06 30`) followed by a
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1584-byte payload.
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### Basic Electrical (always present)
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| Offset | Type | Field | Example |
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|--------|---------|------------------|---------|
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| 0-7 | — | Reserved (zero) | — |
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| 8 | float32 | Voltage | 230.30 V|
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| 12 | float32 | Current | 0.065 A |
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| 16 | float32 | Active power | 8.406 W |
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| 20 | float32 | Frequency | 50.02 Hz|
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| 24 | float32 | Power factor | 0.558 |
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### Waveforms (when harmonics enabled, offset 28-543)
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| Offset | Type | Count | Field |
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|---------|--------------|-------|------------------------|
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| 30-285 | int16 LE | 128 | Voltage waveform |
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| 286-541 | int16 LE | 128 | Current waveform |
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Each waveform contains 128 signed 16-bit samples representing one complete
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AC cycle.
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### Voltage Harmonics (when harmonics enabled, offset 544-747)
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| Offset | Type | Count | Field |
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|---------|--------------|-------|----------------------------|
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| 544-740 | float32 | 50 | H1..H50 voltage (% of H1) |
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| 744 | float32 | 1 | UThd (%) |
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H1 = 100.0%. H*n* is at offset `544 + (n-1) * 4`.
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### Current Harmonics (when harmonics enabled, offset 800-1003)
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| Offset | Type | Count | Field |
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|---------|--------------|-------|----------------------------|
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| 800-996 | float32 | 50 | H1..H50 current (% of H1) |
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| 1000 | float32 | 1 | AThd (%) |
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H1 = 100.0%. H*n* is at offset `800 + (n-1) * 4`.
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### Harmonics Detection
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When harmonics is disabled, offsets 28+ are all zero. To detect whether
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harmonics data is present, check if the float32 at offset 544 equals 100.0
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(H1 voltage fundamental = 100%).
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## Power Supply Control
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### Output On/Off (`8C 72`)
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```
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TX: 8C 72 00 -> Output ON
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TX: 8C 72 01 -> Output OFF
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RX: 8C 72 -> ACK
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```
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The PSU output must be turned on before taking measurements.
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### Output Mode (`8C 7A`)
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```
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TX: 8C 7A 00 -> AC mode
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TX: 8C 7A 01 -> DC mode
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RX: 8C 7A -> ACK
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```
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### AC Parameters (`8C 78`)
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```
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TX: 8C 78 00 <float32 LE> -> Set voltage (V), range 100-240
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TX: 8C 78 01 <float32 LE> -> Set frequency (Hz), 50 or 60
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RX: 8C 78 -> ACK
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```
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### DC Parameters (`8C 73`)
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```
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TX: 8C 73 00 <float32 LE> -> Set current limit (A), range 0-5
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TX: 8C 73 01 <float32 LE> -> Set voltage (V), range 1-60
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RX: 8C 73 -> ACK
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```
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### Read Settings (`8C 79`)
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20-byte response: `8C 79` + 18 bytes payload.
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| Offset | Type | Field |
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|--------|---------|--------------------|
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| 0 | float32 | AC voltage (V) |
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| 4 | float32 | AC frequency (Hz) |
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| 8 | float32 | DC voltage (V) |
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| 12 | float32 | DC current (A) |
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| 16 | uint8 | Mode (0=AC, 1=DC) |
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| 17 | uint8 | Marker (0xFF) |
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### Integration Time (`8C 01`)
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```
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TX: 8C 01 <uint32 LE> -> Integration time in microseconds
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RX: 8C 01 -> ACK
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```
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Common values: 200000 (200 ms), 500000 (500 ms), 1000000 (1000 ms).
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## Identify (`8C 00`)
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16-byte response: `8C 00` + `"HPCS6500\0\0"` + 4 bytes device metadata.
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## Notes
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- The instrument computes all photometric, colorimetric, and radiometric
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values internally. The host software only reads and displays results.
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- During continuous measurement, the host polls `8C 03` and reads `8C 13`
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+ `8C 77` on each cycle (~550 ms per reading).
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- All float values are IEEE 754 single-precision (4 bytes), little-endian.
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- All integer values are unsigned little-endian unless noted (waveform
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samples are signed int16).
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Reference in New Issue
Block a user