DSP56303 datasheet(208/292 Pages) FREESCALE

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DSP56303 User’s Manual, Rev. 2

9-16

Freescale Semiconductor

Triple Timer Module

9.3.3 Pulse Width Modulation

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.

Bit Settings

Mode Characteristics

TC3

TC2

TC1

TC0

Mode

Name

Function

TIO

Clock

Pulse width modulation

PWM

Output

Internal

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