# LP5562EVM MSP430 Serial Protocol (Reverse-Engineered)

**Date**: 2026-03-05
**Status**: Working — I2C read/write verified, LEDs cycling

## Hardware

- **EVM**: LP5562EVM (SNVU203A) with MSP430F5510 USB-to-I2C bridge
- **USB**: CDC device, VID:PID `2047:0300`, appears as `/dev/ttyACM0`
- **Baud**: 115200, 8N1
- **EN pin**: Must be jumpered to VDD externally — MSP430 does NOT drive EN after reset

## Protocol

Commands are ASCII text, no line terminator needed. The MSP430 parses character-by-character and responds after receiving the expected number of hex digits.

### Commands

| Command | Format | Response | Description |
|---------|--------|----------|-------------|
| `?` | `?` | `TI Sep 12 2012 08:19:25\n` | Firmware version |
| `I` (read) | `I<addr2><reg2>` | `SS DD OK\n` | I2C register read |
| `O` (write) | `O<addr2><reg2><data2>` | `SS OK\n` | I2C register write |
| `R` (read) | `R<addr2><reg2>` | `OK\n` | I2C read (no data returned) |
| `A` | `A` | `OK\n` | Unknown (possibly internal) |

- `addr2`: 2-char hex I2C 7-bit address (e.g., `30` for LP5562)
- `reg2`: 2-char hex register address
- `data2`: 2-char hex data byte
- `SS`: 2-char hex status (`00` = success, `02` = I2C NAK / device not responding)
- `DD`: 2-char hex data byte read from device

### Other Command Prefixes

These accept input but are not fully understood:

| Prefix | Chars consumed | Response | Guess |
|--------|---------------|----------|-------|
| `S` | 2 hex chars | (silent) | GPIO/setting control? |
| `V` | 2 hex chars | (silent) | Voltage/value setting? |
| `C` | 6 hex chars | `OK\n` | Config/control? |
| `P` | 8 hex chars | (silent or `OK`) | Program memory? |

### Invalid Commands

Single characters not recognized as command prefixes return `?\n`. Extra characters after a complete command also return `?\n` each.

## LP5562 Register Quirks via EVM Bridge

| Register | Address | Writable | Read-back | Notes |
|----------|---------|----------|-----------|-------|
| ENABLE | 0x00 | Yes | Yes | |
| OP_MODE | 0x01 | Yes | Yes | |
| B/G/R/W_PWM | 0x02-0x05 | Yes | Yes | |
| B/G/R_CURRENT | 0x06-0x08 | Yes | Yes | |
| W_CURRENT | 0x09 | No | Always 0x00 | Write ACKs but no effect |
| CONFIG | 0x0B | Functional | Always 0x00 | Write-only: takes effect but reads 0 |
| STATUS | 0x0C | N/A | Yes | Read-only |
| LED_MAP | 0x70 | Yes | Yes | Default 0x39 (engines mapped) — must set to 0x00 for direct PWM |

## Working Init Sequence

```
O300DFF     # Reset (write 0xFF to RESET register)
            # Wait 500ms
O300040     # ENABLE = 0x40 (chip_en)
            # Wait 1ms (>500us startup)
O300B01     # CONFIG = 0x01 (internal oscillator) — write-only
O307000     # LED_MAP = 0x00 (all channels = I2C direct)
O300632     # B_CURRENT = 0x32 (5mA)
O300732     # G_CURRENT = 0x32
O300832     # R_CURRENT = 0x32
            # W_CURRENT left at default 0xAF (0x09 not writable)
O3002FF     # B_PWM = 0xFF (full brightness)
```

## LED Hardware on EVM

- **D1**: LRTB_G6SF (Osram RGB LED) — driven by B/G/R channels
- **D2-D5**: LW Q38E (Osram white LEDs) — driven by W channel
- **D7**: LSL296 (red status LED) — driven by MSP430, not LP5562
- All LP5562 LED outputs pass through **P5** header (4x2 dual-row with jumpers)

## Key Discovery: EN Pin

The LP5562 EN pin is controlled by the MSP430's GPIO (EN-UC), connected through the P6 header. After USB reset, the MSP430 holds EN low. The TI Windows GUI software presumably sends a command to assert EN, but we were unable to identify which serial command does this.

**Workaround**: Jumper EN directly to VDD (3.3V) on P1 or P6 header. This is acceptable because in the final xblink design, EN is controlled by a wired-AND circuit (MCU GPIO + hall sensor), not the EVM's MSP430.

Without EN high, all I2C reads return status `02` (NAK) with data `00`.

## Using EVM with External MCU (XIAO M0)

When driving the LP5562 from an external MCU instead of the MSP430:

1. **Disconnect EVM from USB** — the MSP430 must be unpowered to avoid I2C bus contention.
2. **P6 header**: Remove the **EN jumper** to disconnect EN-UC (MSP430's EN output). Leave SCL/SDA jumpers in place — the unpowered MSP430's I/O pins go high-impedance.
3. **P4 header**: Feed external VDD (e.g., XIAO 5V pin → P4 VDD). The on-board LP2985 3.3V LDO only runs from USB power.
4. **Wiring**: XIAO A0 → P6 EN (LP5562 side), A4 → SDA, A5 → SCL, GND → GND, 5V → VDD.

The LP5562 VDD range is 2.7–5.5V. Using 5V ensures headroom for white LED forward voltage (~3.0V) plus LP5562 current sink saturation (~0.4V).