My understanding is that when the needed quantities of higher speed rated testing chips are done, the rest of the same identical parts are tested at the lower clock speed and then sold as the slower part. Most all probably *would* test OK at the higher speeds. All are identically constructed on the same equipment, no electrical or physical differences (the occasional die shrink happens occasionally, but that happens to ALL the parts, not just the higher speed ones ) They may test at slower speed first, know how to look it up so I don't store that info Remember: this testing is done over *all* guaranteed supply voltages and *all* temperatures, not just the nominal power supply voltage and temperature you probably use the chip at - So yes, you can overclock. Do so with care, though. Works for prototypes and "play projects", I certainly would not do this for ANY life-critical projects, too much liability for saving a few dollars; OTOH, by adding a heat sink, there are reportedly people who can run a 20MHz part WAY overclocked, and reportedly don't have problems (in their commercial application, that their livelihood depends on.) Something like a 20MHz part at 40-50 MHz speeds, which sounds way overclocked to me. I haven't tested this; A Microchip FAE said it, and I DO believe him! Moral of the story: Test your own chips, individually, at the desired speed and over the expected variety of power supply voltages and temperatures it'll run at, if you're going to do this, and you want good reliability; Microchip does make pretty robust chips. Add a nice heat sink if over the max rated speed for that IC, probably. Expect some chips not to work at higher speeds, if rarely. Worry less about a chip run within it's rated speed range (i.e. an F84-04 run at 10MHz) than outside the available speed range (i.e. an F84-04 run at 20MHz.) And, think safety - We all know Murphy's Laws. (My fathers' pellet stove feeds pellets happily, even if the stove's gone out - we've had to dig the entire firebox free of literally gallons unburned pellets, a few times, not a lethal problem, but really QUITE annoying!) If your overclocked PIC fails, what'll the consequences be? Annoying or catastrophic? Probably best to do the same job in a sneakier way with lower speeds, or with different hardware (FPGA/CPLD/other front end) instead of pushing hardware beyond it's limits, if you can. The "Principle of least astonishment" is here on Earth for a good reason, folks Mark Tobie Horswill wrote: > Hi, > > I've just noted that the last batch of PICs I bought (16f84 and 16f877) > were of the 04/P type. I've been running the F84 at 8 Mhz and the F877 at > 20Mhz without any problems, they don't seem to be overheating. > > What's the physical difference between de 4Mhz and the 10 or 20Mhz > versions and do I risk damaging them if they are run overclocked for long > periods ? > > Also, has anyone been able to modify the F877's SSPSTAT<7,6> bits also > known as SMP and CKE ? I'm using MPLAB 5.00 and the simulator refuses to > change these bits (banking is ok). > > Thanks, > > Tobie -- I re-ship for small US & overseas businesses, world-wide. (For private individuals at cost; ask.)