DIGITAL COUNTDOWN TIMER SOFTWARE
DIGITAL COUNTDOWN TIMER DOWNLOAD

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These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. If the time interval expires without the customer's being seated, the timer's display flashes to indicate that a guarantee of service went unmet. In such an application, the restaurant's greeter presses the timer's reset switch to reset the processor and start a preprogrammed countdown interval. Many of the microprocessor's functions and I/O pins remain unused and available for additional features, and the compact firmware for implementing the counter occupies less than 250 bytes of 8 kbytes of available flash memory.Īpplications for the circuit range from exercise-routine timing to a restaurant-service-guarantee timer. Given the device's low current drain, a designer could reduce the timer's cost and complexity by packaging the circuitry along with a nonreplaceable battery. Thus, total current consumption for the digital countdown timer is the sum of the standby- and main-loop currents: 1.8+0.025 1.8 ♚.Īt approximately 1.8-♚ average current consumption, the countdown timer easily meets the 2.28-♚ design goal and ensures more than 10 years of continuous operation. With such a short active period, the main loop's total current consumption is virtually negligible: Main loop=250 mA×(100/1 million)=0.025 ♚.

DIGITAL COUNTDOWN TIMER SOFTWARE

Writing the software to execute 100 or fewer clock cycles-equivalent to 100 µsec at the default 1-MHz CPU clock frequency-reduces current demand. The main loop activates the CPU and its on-chip high-speed oscillator, which consume a total of 250 ♚. If so, the display flashes the time-out message.

DIGITAL COUNTDOWN TIMER DOWNLOAD

(Click here to download the timer software's assembly-language)Īs a final step, the main loop compares the countdown register's contents with zero to determine whether the preprogrammed time interval has expired. As a bonus, this method directly displays the countdown register's contents on the LCD without requiring current-hungry binary-to-BCD conversions. For example, 21+99=120 dropping the one in the 100s place yields a value of 20. Adding a value of 99 (decimal) to the countdown register and discarding the leftmost digit perform a one-digit subtraction. The interrupt awakens the processor, which executes an active main-software loop that decrements a countdown register via direct BCD (binary-coded-decimal) subtraction.

In normal (standby) operation, the microprocessor's 32-kHz external-crystal clock drives an internal counter that generates an interrupt once per second.

Digital countdown timer