Texas Instruments MSP430x1xx Principles for Low-Power Applications, Connection of Unused Pins

Principles for Low-Power Applications

2.4 Principles for Low-Power Applications

Often, the most important factor for reducing power consumption is using the MSP430’s clock system to maximize the time in LPM3. LPM3 power consumption is less than 2 ∝A typical with both a real-time clock function and all interrupts active. A 32-kHz watch crystal is used for the ACLK and the CPU is clocked from the DCO (normally off) which has a 6-∝s wake-up.

-Use interrupts to wake the processor and control program flow.

-Peripherals should be switched on only when needed.

-Use low-power integrated peripheral modules in place of software driven functions. For example Timer_A and Timer_B can automatically generate PWM and capture external timing, with no CPU resources.

-Calculated branching and fast table look-ups should be used in place of flag polling and long software calculations.

-Avoid frequent subroutine and function calls due to overhead.

-For longer software routines, single-cycle CPU registers should be used.

2.5Connection of Unused Pins

The correct termination of all unused pins is listed in Table 2−2.

Table 2−2. Connection of Unused Pins

Pin	Potential	Comment
AVCC	DVCC
AVSS	DVSS
VREF+	Open
VeREF+	DVSS
VREF− /VeREF−	DVSS
XIN	DVCC
XOUT	Open
XT2IN	DVSS	13x, 14x, 15x and 16x devices
XT2OUT	Open	13x, 14x, 15x and 16x devices
Px.0 to Px.7	Open	Switched to port function, output direction
	DVCC or VCC	Pullup resistor 47 kΩ
RST/NMI
Test/VPP	DVSS	P11x devices
Test	DVSS	Pulldown resistor 30K 11x1 devices
	Open	11x1A, 11x2, 12x, 12x2 devices
TDO	Open
TDI	Open
TMS	Open
TCK	Open

System Resets, Interrupts, and Operating Modes 2-17