说明：  This application report describes how to simultaneously create a sine wave, a ramp, and a dc level with pulse-width modulated (PWM) signals from Timer_B on the MSP430 ultralow power family of microcontrollers. PWM signals are often used to create analog signals in embedded applications. This report shows how to create both ac signals and dc levels with PWM outputs. The example in this report uses Timer_B on the MSP430F149, but Timer_A could also be used in a similar manner.