SLAU319AF July 2010 – September 2022
Applying an appropriate entry sequence on the RST/NMI and TEST pins forces the MSP430 MCU to start program execution at the BSL RESET vector instead of at the RESET vector located at address FFFEh.
If the application interfaces with a computer UART, these two pins can be driven by the DTR and RTS signals of the serial communication port (RS232) after passing level shifters. Detailed descriptions of the hardware and related considerations can be found in Section 4. The normal user reset vector at FFFEh is used if TEST is kept low while RST/NMI rises from low to high (standard method, see Figure 1-1).
The BSL program execution starts when the TEST pin has received a minimum of two rising edges (low-to-high transitions) and if TEST is high while RST/NMI rises from low to high (BSL entry method, see Figure 1-2). This level transition triggering improves BSL start-up reliability. The first high level of the TEST pin must be at least tSBW, En (see device-specific data sheet for tSBW, En parameter).
For the MSP430F522x and MSP430F521x split-rail devices with DVIO supply, the entry sequence is applied on the RST/NMI and BSLEN pins. For pin information, refer to the device-specific data sheet. For additional information, refer to the bootloader section in Designing With MSP430F522x and MSP430F521x Devices.
The recommended minimum time for pin states is 250 ns. See the device-specific errata for any differences, because some 5xx and 6xx device revisions require specific entry sequences.
The TEST signal is normally used to switch the port pins between their application function and the JTAG function. In devices with BSL functionality, the TEST and RST/NMI pins are also used to invoke the BSL. To invoke the BSL, the RST/NMI pin must be configured as RST and must be kept low while pulling the TEST pin high and while applying the next two edges (falling and rising) on the TEST pin. The BSL is started after the TEST pin is held low after the RST/NMI pin is released (see Figure 1-2).