xblink/docs/plans/2026-03-05-lp5562evm-protocol.md

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).