110 PCM-5823 User's ManualE.1 Programming the watchdog timerJumper J3 controls the watchdog settings. The default configura-tion of the timer is enabled via a system reset.To enable the watchdog timer, you must write a program whichwrites 1 to I/O port address 443 (hex) at regular intervals. The firsttime your program reads the port, it enables the watchdog timer.After that, your program must write 1 to the port at time interval ofless than 1.6 seconds, otherwise the watchdog timer will activateand reset the CPU or generate an interrupt on IRQ11. When youwant to disable the watchdog timer, your program should write 0to I/O port 443.If CPU processing comes to a standstill because of EMI or asoftware bug, your program's signals to I/O port 443 to the timerwill be interrupted. The timer will then automatically reset theCPU or invoke an IRQ, and data processing will continue normal-ly.You must write your program so that it writes 1 to I/O port 443 atan interval shorter than the timer's preset interval. The timer'sintervals have a tolerance of ± 30%, so you should program aninstruction that will refresh the timer about every second.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
