MSP430FR2433: Unable to Receive BSL ACK Using UART – TEST/RST Sequence

Tool / Software: BSL-Scripter / BSLDEMO
Category: MCU / Bootloader / BSL
Subcategory: UART BSL Entry Issue

Description:

When attempting to invoke the BSL via the standard TEST/RST sequence, the MSP430FR2433 does not respond with the expected 0x90 ACK byte after sending the UART synchronization byte (0x80).

• Either no response is received, or the UART shows garbage data.

• Tested with multiple USB-UART adapters and COM ports.

Steps to Reproduce:

1. Initialize host MCU UART at 9600 bps, 8N1&8E1.

2. Set RST low. Apply TEST high → low → high (two rising edges required).

3. Release RST while TEST is high.

4. Send sync byte 0x80 over UART.

5. Observe expected ACK 0x90 from target.

Observed Behavior:

• Sync byte is transmitted successfully.

• Target does not send ACK (0x90).

• Logic analyzer shows correct TEST/RST waveform.

• UART RX from target remains idle or produces invalid data.

Expected Behavior:

• Target BSL should acknowledge the sync byte with 0x90.

• UART-based programming should be possible.

Methods Tried:

1. BSL Entry via Hardware

   • TEST pin toggled twice while RST held low, TEST kept high, RST released.

   • Verified timing with logic analyzer.

2. BSL Entry via Software

   • Jump to ROM BSL at 0x1000 from running firmware.

3. BSL-Scripter Attempts

   • Script example:

• Observed issues:

  • [ACK_ERROR_MESSAGE] Unknown ACK value after providing wrong password.

Request:

• Guidance on why UART BSL is not responding for MSP430FR2433.

• Confirmation on proper hardware wiring and TEST/RST timing.

• Recommended script commands for mass erase, password handling, and firmware programming.

• Any workarounds or updated tools to make UART BSL functional.