ADSP-BF537 Blackfin Processor Hardware Reference
15-23
General-Purpose Timers
When
CLK_SEL
is set, the counter resets to 0x0 at startup and increments
on each rising edge of
PWM_CLK
. The
TMRx
pin transitions on rising edges
of
PWM_CLK
. There is no way to select the falling edges of
PWM_CLK
. In this
mode, the
PULSE_HI
bit controls only the polarity of the pulses produced.
The timer interrupt may occur slightly before the corresponding edge on
the
TMRx
pin (the interrupt occurs on an
SCLK
edge, the pin transitions on
a later
PWM_CLK
edge). It is still safe to program new period and pulse
width values as soon as the interrupt occurs. After a period expires, the
counter rolls over to a value of 0x1.
The
PWM_CLK
clock waveform is not required to have a 50% duty cycle, but
the minimum
PWM_CLK
clock low time is one
SCLK
period, and the mini-
mum
PWM_CLK
clock high time is one
SCLK
period. This implies the
maximum
PWM_CLK
clock frequency is
SCLK/2
.
The alternate timer clock inputs (
TACLKx
) are enabled when a timer is in
PWM_OUT
mode with
CLK_SEL
=
1
and
TIN_SEL
=
0
, without regard to the
content of the multiplexer control and function enable registers.
Using PWM_OUT Mode With the PPI
Up to three timers are used to generate frame sync signals for certain PPI
modes. For detailed instructions on how to configure the timers for use
with the PPI, refer to
“Frame Synchronization in GP Modes” on
of the PPI chapter.
Stopping the Timer in PWM_OUT Mode
In all
PWM_OUT
mode variants, the timer treats a disable operation (W1C to
TIMER_DISABLE
) as a “stop is pending” condition. When disabled, it auto-
matically completes the current waveform and then stops cleanly. This
prevents truncation of the current pulse and unwanted PWM patterns at
the
TMRx
pin. The processor can determine when the timer stops running
by polling for the corresponding
TRUNx
bit in the
TIMER_STATUS
register to
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...