Advantages of Using a MicroMonitor and a Simple Application Demonstrating the

Advantages of Using a MicroMonitor and a Simple Application Demonstrating the Use of a DS1232

Introduction
Dallas Semiconductor’s DS1232 MicroMonitor chip is a highly integrated solution to add power-on reset
delay, a pushbutton reset controller, robust power failure monitoring, and watchdog timer functionality to
your microprocessor system with the addition of a single chip. The chip also offers both active and low reset
signals, and selectivity of the watchdog time out period and the voltage monitoring level. The high level of
integration reduces both the cost of implementation and the board space required. The chips are available in
several packages including 8-pin mSOP, SOIC, and DIP.
Advantages of Using a Dallas Semiconductor DS1232 MicroMonitor
Power-on Reset Delay Allows Board Resources to Stabilize Before Execution Begins
Precise control of a microcontroller’s reset pin is important at all times during the operation of a circuit.
Thus, it is imperative that the reset pin is controlled during both normal operation and during the power-up
time of the circuit. One common problem with many microprocessor circuits is that the microcontroller
begins execution before the memory and I/O resources available to it have a stable power supply. Some chips
require hundreds of milliseconds to reset themselves and ready for operation. If a microprocessor begins
execution within microseconds of a reset, it could be executing based on invalid input from the system
resources. This can be resolved by adding a power-on reset (POR) circuit that holds the microprocessor in
reset during the power-up sequence for 100s of milliseconds after a reset occurs. The DS1232 will hold a
microcontroller’s reset pin active for a minimum time of 250ms (typically 610 ms.) Additionally, it can
provide either an active high or active low reset, which makes it compatible with any microprocessor.
Pushbutton Reset Circuit Debounces a Momentary Switch and Provides a Solid Reset Pulse
Another common problem in microprocessor circuits is that a less than perfect reset signal causes the
microprocessor to reset several times, possibly executing some fragment of the initialization routine several
times before the reset finally stabilizes. In some circuits this is trivial. However, in other circuits this could
cause major system problems. The DS1232 has internal circuitry that debounces a push-button and provides
the system a clean reset signal. This eliminates the need to have both a separate power-on reset circuit and
pushbutton circuitry attached separately to the reset pin. Plus, the DS1232 will hold the reset pin low for at
least 250 ms to guarantee that the manual reset is received correctly by the microprocessor every time.
The DS1232 Provides Power Failure Monitoring
Brownouts and power failures are a reality for most microprocessor systems. Since there is no way to avoid
the occasional power cycle, a robust microprocessor solution must account for the various power failure
modes. The DS1232 monitors the power supply to a microprocessor and forces the microprocessor into its
reset state if there is a brownout or if the power fails altogether. This guarantees that the system will not try
to operate during irregular supply voltage conditions, and it can prevent the microprocessor from executing
code when it should really be waiting for the supply voltage to return to a valid state.

It
Watchdog timers are used to ensure that if the code operating on a microprocessor enters into an
unanticipated state, then the processor will reset after some minimal amount of time elapses. Many
microprocessors have an internal watchdog timer that handles this function without an external component.
However, the internal watchdog timer can be disabled by the pseudo-random code that is executing on the
microprocessor. The external watchdog timer on the DS1232 cannot be disabled. This gives you peace of
mind, knowing that if the MicroMonitor is not strobed, then the microcontroller will be reset. Another nice
feature of the DS1232 is that the strobe period can be varied to one of three different values. The device thus
works well with faster and slower microprocessors because you can program the watchdog timer to an
appropriate rate for any microcontroller. Another advantage of the external watchdog timer is that the strobe
signal is visible to the external world because it is on an I/O pin. This allows easier debugging of watchdogrelated
problems.
Hardware Required for Using a DS1232 with a Microcontroller
The greatest asset of the DS1232 is that all of the functions listed above are implemented in a single package.
This functionality does not require a complex chipset. The schematic below shows how the DS1232 is used
with a Dallas Semiconductor DS87C520 Microcontroller. Since most systems incorporate a pushbutton reset,
the only things added are the DS1232, a pull-up resistor for the active low output, and a decoupling capacitor
to reduce the possibility of noise on the power supply causing a reset. The pull-up resistor is added here
because it is used to generate the oscilloscope plots shown on the following pages. The RST output of the
DS1232 is not required by the DS87C520. The LEDs on the diagram are used to signal when ISRs (Interrupt
Service Requests) are being serviced.

DyPryFDO.pdf (151.27 KB, 下载次数: 0 )