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michael 5970a21b54 Add LP5562EVM USB-I2C control tool, document reverse-engineered protocol 
Reverse-engineered the MSP430 serial protocol on the LP5562EVM:
- I<addr><reg> reads, O<addr><reg><data> writes, status 00=OK / 02=NAK
- EN pin must be jumpered to VDD (MSP430 doesn't drive it after reset)
- CONFIG (0x0B) is write-only, W_CURRENT (0x09) not writable via bridge
- LED cycling verified: all 4 channels respond to direct PWM control

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-03-05 11:11:35 -08:00

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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.