ADSP-BF522 AD [Analog Devices], ADSP-BF522 Datasheet - Page 10

• Manufacturer Part Number: ADSP-BF522
• Description: Blackfin Embedded Processor
• Manufacturer: AD [Analog Devices]

ADSP-BF522/523/524/525/526/527
REAL-TIME CLOCK
The real-time clock (RTC) provides a robust set of digital watch
features, including current time, stopwatch, and alarm. The
RTC is clocked by a 32.768 kHz crystal external to the
Blackfin processor. The RTC peripheral has dedicated power
supply pins so that it can remain powered up and clocked even
when the rest of the processor is in a low-power state. The RTC
provides several programmable interrupt options, including
interrupt per second, minute, hour, or day clock ticks, interrupt
on programmable stopwatch countdown, or interrupt at a pro-
grammed alarm time.
The 32.768 kHz input clock frequency is divided down to a 1 Hz
signal by a prescaler. The counter function of the timer consists
of four counters: a 60-second counter, a 60-minute counter, a
24-hour counter, and an 32,768-day counter.
When enabled, the alarm function generates an interrupt when
the output of the timer matches the programmed value in the
alarm control register. There are two alarms: The first alarm is
for a time of day. The second alarm is for a day and time of
that day.
The stopwatch function counts down from a programmed
value, with one-second resolution. When the stopwatch is
enabled and the counter underflows, an interrupt is generated.
Like the other peripherals, the RTC can wake up the processor
from sleep mode upon generation of any RTC wakeup event.
Additionally, an RTC wakeup event can wake up the processor
from deep sleep mode or cause a transition from the hibernate
state.
Connect RTC pins RTXI and RTXO with external components
as shown in
WATCHDOG TIMER
The processor includes a 32-bit timer that can be used to imple-
ment a software watchdog function. A software watchdog can
improve system availability by forcing the processor to a known
state through generation of a hardware reset, nonmaskable
interrupt (NMI), or general-purpose interrupt, if the timer
SUGGESTED COMPONENTS:
X1 = ECL IPTEK EC38J (THROUGH-HOLE PACKAGE) OR
C1 = 22 pF
C2 = 22 pF
R1 = 10 M
NOTE: C1 AND C2 ARE SPECIFIC TO CRYSTAL SPECI FIED FOR X1.
CONTACT CRYSTAL MANUFACTURER FOR DETAILS. C1 AND C2
SPECIFICATIONS ASSUME BOARD TRACE CAPACITANCE OF 3 pF.
EPSON MC405 12 pF LOAD (SURFACE-MOUNT PACKAGE)
Figure
C1
RTXI
Figure 4. External Components for RTC
4.
R1
X1
C2
RTXO
Rev. PrG | Page 10 of 80 | February 2009
expires before being reset by software. The programmer initial-
izes the count value of the timer, enables the appropriate
interrupt, then enables the timer. Thereafter, the software must
reload the counter before it counts to zero from the pro-
grammed value. This protects the system from remaining in an
unknown state where software, which would normally reset the
timer, has stopped running due to an external noise condition
or software error.
If configured to generate a hardware reset, the watchdog timer
resets both the core and the processor peripherals. After a reset,
software can determine if the watchdog was the source of the
hardware reset by interrogating a status bit in the watchdog
timer control register.
The timer is clocked by the system clock (SCLK), at a maximum
frequency of f
TIMERS
There are nine general-purpose programmable timer units in
the processors. Eight timers have an external pin that can be
configured either as a pulse width modulator (PWM) or timer
output, as an input to clock the timer, or as a mechanism for
measuring pulse widths and periods of external events. These
timers can be synchronized to an external clock input to the sev-
eral other associated PF pins, an external clock input to the
PPI_CLK input pin, or to the internal SCLK.
The timer units can be used in conjunction with the two UARTs
to measure the width of the pulses in the data stream to provide
a software auto-baud detect function for the respective serial
channels.
The timers can generate interrupts to the processor core provid-
ing periodic events for synchronization, either to the system
clock or to a count of external signals.
In addition to the eight general-purpose programmable timers,
a ninth timer is also provided. This extra timer is clocked by the
internal processor clock and is typically used as a system tick
clock for generation of operating system periodic interrupts.
UP/DOWN COUNTER AND THUMBWHEEL
INTERFACE
A 32-bit up/down counter is provided that can sense 2-bit
quadrature or binary codes as typically emitted by industrial
drives or manual thumb wheels. The counter can also operate in
general-purpose up/down count modes. Then, count direction
is either controlled by a level-sensitive input pin or by two edge
detectors.
A third input can provide flexible zero marker support and can
alternatively be used to input the push-button signal of thumb
wheels. All three pins have a programmable debouncing circuit.
An internal signal forwarded to the timer unit enables one timer
to measure the intervals between count events. Boundary regis-
ters enable auto-zero operation or simple system warning by
interrupts when programmable count values are exceeded.
SCLK
.
Preliminary Technical Data