Clever use of memory units can actually improve your products. Need to extend your staff's productiveness? Cut back Bugs? Meet deadlines? Take Jack's in the future Better Firmware Quicker seminar. You’ll learn how to estimate a schedule accurately, thwart schedule-killing bugs, handle reuse, construct predictable real-time code, better ways to deal with uniquely embedded problems like reentrancy, heaps, stacks and hardware drivers, and far, way more. Jack might be presenting this seminar in Chicago (April 23, 2008), Denver (April 25) and London, UK (May 19). Wish to be your company’s embedded guru? Join us! More info here. For hints, methods and ideas about better ways to construct embedded techniques, subscribe to The Embedded Muse, a free biweekly e- e-newsletter. No advertising, simply down to earth embedded discuss. Click right here to subscribe. In my October column I wrote about eliminating potentiometers from embedded methods, replacing them with sensible software to routinely compute calibration values. Tis a noble endeavor, this removal of analog components. But, the place will we retailer the calibration coefficients?
The nice attraction of a potentiometer is its potential to "retailer" an analog value. Once set, it provides a constant voltage or current whose value is decided by its shaft's position. The value is remembered even when the system is deprived of energy for long intervals. Given that most embedded methods don't embody traditional mass storage units like disks, we'll have to search out some manner to avoid wasting our digital pot equivalent data. Memory Wave Experience is the obvious selection, but information stored in RAM is misplaced when power is removed. AT and 386 class machines all embrace a "setup" program that determines basic working parameters like disk dimension and configuration. This information is normally saved in standard low power RAM, whose contents are maintained utilizing a easy battery circuit. When energy goes down, the battery takes over. Most CMOS static RAMs enter an ultra low power standby mode when not selected. Often, they'll maintain their contents even at 2 to 3 volt Vcc levels, so two or three AA cells provides more than sufficient voltage to maintain the data intact.
There are a number of battery-backed up systems around. Quite just a few suffer from poor design which exhibits itself by occasional data dropouts. This is unforgivable: nobody, however no one, messes with my knowledge! When my three 12 months old destroyed the dishwasher, I could perceive. When he broke the VCR, I figured that, effectively, he has to study even at the expense of some electronics. But then he innocently disassembled a floppy disk - that was laborious to forgive! Most designs isolate the RAM's predominant energy supply from the battery circuit using a diode or equal transistor circuit. Without the diode, when power is down the battery will be called on to run your complete computer. Silicon diodes have a junction drop equal to round .7 volts. A 5.Zero volt supply might be solely 4.Three or so when measured on the diode's cathode. Whereas greater than sufficient to retain knowledge, it is lower than needed to run the RAM throughout normal operation.
Anything less than 4.Seventy five volts is simply too low. Unfortunately, most RAMs will more or less run with Vcc below specification, so these circuits generally appear to work