Motorola DSP56301 user manual Pulse Width Modulation PWM, Mode, Pwm, Pulse width modulation

Operating Modes

9.3.3Pulse Width Modulation (PWM, Mode 7)

	Bit Settings				Mode Characteristics
TC3	TC2	TC1	TC0	Mode	Name	Function	TIO	Clock
0	1	1	1	7	Pulse width modulation	PWM	Output	Internal

In Mode 7, the timer generates periodic pulses of a preset width. When the counter equals the value in the TCPR, the TIO output signal is toggled and TCSR[TCF] is set. The contents of the counter are placed into the TCR. If the TCSR[TCIE] bit is set, a compare interrupt is generated. The counter continues to increment on each timer clock.

If counter overflow occurs, the TIO output signal is toggled, TCSR[TOF] is set, and an overflow interrupt is generated if the TCSR[TOIE] bit is set. If the TCSR[TRM] bit is set, the counter is loaded with the TLR value on the next timer clock and the count resumes. If the TCSR[TRM] bit is cleared, the counter continues to increment on each timer clock. This process repeats until the timer is disabled.

When the TCSR[TE] bit is set and the counter starts, the TIO signal assumes the value of INV. On each subsequent toggle of the TIO signal, the polarity of the TIO signal is reversed. For example, if the INV bit is set, the TIO signal generates the following signal: 1010. If the INV bit is cleared, the TIO signal generates the following signal: 0101.

The value of the TLR determines the output period ($FFFFFF − TLR + 1). The timer counter increments the initial TLR value and toggles the TIO signal when the counter value exceeds $FFFFFF. The duty cycle of the TIO signal is determined by the value in the TCPR. When the value in the TLR increments to a value equal to the value in the TCPR, the TIO signal is toggled. The duty cycle is equal to ($FFFFFF – TCPR) divided by ($FFFFFF − TLR + 1). For a 50 percent duty cycle, the value of TCPR is equal to ($FFFFFF + TLR + 1)/2.

Note: The value in TCPR must be greater than the value in TLR.

Triple Timer Module 9-19