Damn dude! Awesome answer. Thanks! I had asked since I run my 16F872's at 4Mhz and found that the F's were $2.83 (actually 20Mhz versions), and the LF's were $2.98. Each in 25-piece qty's from Digi- key. $0.16 seemed like a no brainer case for the LF's, but now it all makes sense. Cheers, -Neil. -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Mark J. Dulcey Sent: Wednesday, July 10, 2002 1:35 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: Small battery backup? Pic Dude wrote: > Looking at the specs & prices for the LF vs F parts, I'm not sure > what the advantage is in picking up F parts. Seems like the LF > will do everything the F will, but has the advantage of lower > power, lower voltage, etc. So why would they even bother to make > the F parts? The LF chips are identical to the F parts, except that they passed their tests all the way down to 2 volts. Parts sold as F chips may have failed some low voltage tests, or may have never been tested at low voltage. Not all PICs make the grade at the low voltage; they may fail completely, or only intermittently. Also, the additional low voltage testing takes additional time, which slightly increases the production cost. Only a few customers are willing to pay a premium for low voltage parts, so if Microchip has already filled their quota for LF parts, and they have more PICs available, the additional chips probably won't be tested at the full voltage range. Similarly, the 4 MHz parts are likely to be chips that failed testing at 20 MHz. But some of them will simply never have been tested at 20 MHz, or might have even passed! There is a demand for minimum-cost parts, especially from high-volume customers; if Microchip doesn't have enough parts that fail the 20 MHz testing to meet demand for 4 MHz chips, they may simply mark some perfectly good 20 MHz chips as 4 MHz and sell them at the lower price, as it is better than not selling them at all. The same logic also applies to the commercial (0 to 70C), industrial (-40 to 85C), and extended (-40 to 125C) temperature grades. Commercial grade chips may have failed at high or low temperature, but they also might have passed. Chip makers have been doing this kind of quality grading for many years; it's not unique to Microchip. It would appear that Microchip's processes have improved; some of the newest PICs (16F877A, the 18F series) don't come in low-speed grades, suggesting that they no longer have a significant number of chips that fail to work at full speed. Similarly, the 18F parts don't come in commercial temperature grade; only industrial and extended. What this means is that some of the chips sold as lower grade parts (4 MHz parts or not LF) will work perfectly at low voltage or full speed. Microchip just won't guarantee that they will work. If you're building a prototype, and you don't have the right grade of chip on hand, go right ahead and try the wrong one; it's likely to work. But if you're going into production, use the right parts; you'll be happier in the long run. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu