7.4. MSP430 RESETS 221
level indication. The maskable interrupts, as the name indicates, are those requests, if necessary, that
can be masked (ignored) by the CPU. The maskable interrupts require a programmer to activate the
interrupts by writing to speciﬁc registers.
7.4 MSP430 RESETS
The Brownout reset is triggered by four different events. The ﬁrst one occurs when power is applied
to the controller when it was turned off. One can simulate the power up event also by supplying
a low signal to the
RT S/NMI pin, which is the second event. The RT S/NMI pin is conﬁgured
as the reset pin as the default setting designated with the SYSNMI bit in the SFRRPCR (Special
Function Register Reset Pin Control Register) shown in Figure 7.1. Note that a programmer can also
conﬁgure the pin to enable and disable (SYSRSTRE – Reset pin resistor enable and SYSRSTUP
– Reset resistor pin pullup/pulldown) pullup or pulldown registers connected to the pin as well as
assigning a particular logic level (SYSNMIEES – NMI edge select bit) to trigger the reset using this
register. This pin is connected to the reset button on all of the MSP430 evaluation boards. The third
possible event that can cause the BOR is when the MSP430 controller wakes up from operating
mode LPM3.5 or LPM4.5. Finally, the last event that triggers the BOR is software BOR events.
For some applications, it is desired to trigger a Brownout reset using a software instruction. Setting
PMMSWBOR (Power Management Module SoftWare BOR) bit in the PMMCTL0 register
(Power Management Module Control Register 0) initiates a software generated BOR.
5HVHUYHG 5HVHUYHG5HVHUYHG5HVHUYHG 6<65675( 6<656783 6<610,,(6 6<610,
Figure 7.1: Special Function Register Reset Pin Control Register.
The second type of reset, the Power-On Reset (POR), is automatically triggered when the
BOR occurs as shown in Figure 7.2. The POR is typically associated with the hardware system
while the Power-Up Clear (PUC) reset is generally linked to software events. In addition to a BOR
event, the POR is triggered by the Power Management Module (PMM) when it detects the power
level of the controller (Supply Voltage Supervisor) falls below a threshold value or a software POR
event. The PUC reset is initiated by six events. The ﬁrst one is the POR event. Whenever the
controller detects a POR, the PUC reset is also triggered. The second and the third reset events for