SLAU319AF July 2010 – September 2022
The two pins used to invoke the bootloader software of the MSP430 MCU— RST/NMI and TEST or TCK (for devices without a dedicated TEST pin)—are controlled by the DTR and RTS signals, respectively. These signals also deliver a positive voltage to supply the bootloader hardware.
For devices with a dedicated TEST pin, the levels at RST/NMI and TEST during normal operation are logic 1 and logic 0, respectively. To achieve these levels and to use the corresponding RS-232 signals as power-supply lines, it is necessary to use two inverters (IC1A, IC2B) for the RST/NMI pin and one inverter (IC2E) for the TEST pin.
Devices without the TEST pin require the inverted TEST pin sequence on their TCK pin to invoke the bootloader. Thus, the corresponding signal is inverted (inverter IC2F).
Diodes prevent discharge of capacitor C1 to allow control of the RS-232 lines (RTS and DTR).