Motorola DSP56309 User Manual page 265

Triple Timer Module
Timer Operational Modes
9.4.3 Pulse 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 PWM Output Internal
Modulation
In this mode, the timer generates periodic pulses of a preset width.
Set the TE bit to clear the counter and enable the timer. The value to which the timer is to
count is loaded into the TPCR. When first timer clock is received from either the
DSP56309 internal clock divided by two (CLK/2) or the prescaler clock output, the
counter is loaded with the TLR value. Each subsequent timer clock increments the
counter.
When the counter equals the value in the TCPR, the TIO output signal is toggled and the
TCF bit in the TCSR is set. The contents of the counter are placed into the TCR. If the
TCIE bit is set, a compare interrupt is generated. The counter continues to be
incremented on each timer clock.
If counter overflow has occurred, the TIO output signal is toggled, the TOF bit in TCSR
is set, and an overflow interrupt is generated if the TOIE bit is set. If the TRM bit is set,
the counter is loaded with the TLR value on the next timer clock and the count is
resumed. If the TRM bit is cleared, the counter continues to be incremented on each
timer clock.
This process is repeated until the timer is disabled by clearing the TE bit.
TIO signal polarity is determined by the value of the INV bit. When the counter is
started by setting the TE bit, the TIO signal assumes the value of the INV bit. On each
subsequent toggling 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 counter contents can be read at any time by reading the TCR.
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.
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