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Maxim > Design Support > Technical Documents > Application Notes > Microprocessor Supervisor Circuits > APP 581
Keywords: power on reset, por, push-button reset, manual reset, debounced, power fail, watchdog timer,
strobe timer, selectable reset timeout, reset threshold, programming 8051, microprocessor supervisor
APPLICATION NOTE 581
Advantages of Using a MicroMonitor and a Simple
Application Demonstrating the Use of a DS1232
May 17, 2001
Abstract: Discusses how the DS1232 can be used to MicroMonitor an 8051-based system. This
supervisor circuit provides power-on-reset (POR), manual reset (push-button) input, a watchdog timer
(strobe timer), and an early power-fail comparator. The reset threshold tolerance can set selected to
monitor both 5% and 10% supply tolerance systems. In addition, a pin-selectable reset time-out delay is
available.
To simplify the use of the device, a software execution program is included to show how the 8051
processor can be used in conjunction with the DS1232.
Introduction
Maxim'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.
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