MSP430 devices that have the fuse on the TEST terminal have a fuse check mode that tests the continuity of the fuse the first time the JTAG port is accessed after a power-on reset (POR). When activated, a fuse check current, ITF , of 1 mA at 3 V or 2.5 mA at 5 V can flow from the TEST pin to ground if the fuse is not burned. Care must be taken to avoid accidentally activating the fuse check mode and increasing overall system power consumption.
When the TEST pin is again taken low after a test or programming session, the fuse check mode and sense currents are terminated.
Activation of the fuse check mode occurs with the first negative edge on the TMS pin after power up or if TMS is being held low during power up. The second positive edge on the TMS pin deactivates the fuse check mode. After deactivation, the fuse check mode remains inactive until another POR occurs. After each POR, the fuse check mode has the potential to be activated.
The fuse check current flow only when the fuse check mode is active and the TMS pin is in a low state (see Figure 6-16). Therefore, the additional current flow can be prevented by holding the TMS pin high (default condition).
The CODE and RAM data protection is ensured if the JTAG fuse is blown.