Modes of Operation
15-34
ADSP-BF537 Blackfin Processor Hardware Reference
overflowed and
PERIOD_CNT = 0
, the
TIMERx_PERIOD
and
TIMERx_WIDTH
registers were updated only if a trailing edge was detected at a previous
measurement report.
Software can count the number of error report interrupts between mea-
surement report interrupts to measure input signal periods longer than
0xFFFF FFFF. Each error report interrupt adds a full 2
32
SCLK
counts to
the total for the period, but the width is ambiguous. For example, in
the period is 0x1 0000 0004 but the pulse width could be
either 0x0 0000 0002 or 0x1 0000 0002.
The waveform applied to the
TMRx
pin is not required to have a 50% duty
cycle, but the minimum
TMRx
low time is one
SCLK
period and the mini-
mum
TMRx
high time is one
SCLK
period. This implies the maximum
TMRx
input frequency is
SCLK/2
with a 50% duty cycle. Under these conditions,
the
WDTH_CAP
mode timer would measure
Period = 2
and
Pulse Width = 1
.
Autobaud Mode
In
WDTH_CAP
mode, some of the timers can provide autobaud detection for
the Universal Asynchronous Receiver/Transmitter (UART) and Control-
ler Area Network (CAN) interfaces. The timer input select (
TIN_SEL
) bit
in the
TIMERx_CONFIG
register causes the timer to sample the
TACIx
pin
instead of the
TMRx
pin when enabled for
WDTH_CAP
mode. Autobaud detec-
tion can be used for initial bit rate negotiations as well as for detection of
bit rate drifts while the interface is operation. For details with the UART
interface, see
Chapter 13, “UART Port Controllers”
CAN interface, see
External Event (EXT_CLK) Mode
Use the
EXT_CLK
mode, sometimes referred to as the “counter mode,” to
count external events, that is, signal edges on the
TMRx
pin which is an
input in this mode.
shows a flow diagram for
EXT_CLK
mode.
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 ...