Re: PIC 16F84 overclocking by Mark Willis .

In building embedded system RTOS's {Real Time OS's} for safety avionics, you will ALWAYS (AFAIK) see a bunch of routines in there that specifically test each and every opcode the processor has, the real-time OS will schedule these one after another "in the background", so only one to ten opcodes get tested every "timeslice", but all get tested inside of a second or so <g> (Details depend on system design, of course!) You also do things like checksumming system ROM and re-testing that checksum, a chunk at a time, testing address lines for shorts/opens, etc. etc. This might be a good way to more thoroughly test here for overclocking - also, adding a heat sink would probably be a good way to improve overclocked characteristics of a PIC (I've heard from my Microchip FAE about someone running a 20 MHz chip at 50 MHz IIRC, with a *good* heat sink.) Thermal grease would be good, too, if messy on a /JW part! <G> Speed isn't always king, IMHO, but overclocking isn't evil either IMHO. Mark Sam Laur wrote: {Quote hidden}> > There was recently some talk about what a 16F84 could do, in speed. So I made > a simple test program (toggle a bit in PORTB to drive a LED, with a delay > loop), and made a simple test jig. Note that the sample is statistically > rather small (insignificant) and comes from the same lot (date code 9809SAN), > so your mileage may vary greatly. > > First, I tested with crystals. Started out using the HS oscillator, but when > some individuals failed to work at 16 MHz, I tried the XT oscillator for fun. > And it seemed to work after that... Most of them could also be pushed to > 18 MHz but 20 MHz wouldn't work with any of the processors that I tried it on. > > The second test was a bit more scientific. I took an RF signal generator, > hooked it up to a simple transistor amplifier stage, and that through a > couple inverter stages (in a 74HC04) to make the signal neat and square. > Then it was only a matter of turning the knob to find out how fast it would > go. I just did this five minutes ago, so I've not had a chance to test it > with more than one processor; I found out with this individual, that it > would operate up to 18.8 MHz, then start acting erratically (LED flashes > irregularly), then stop working altogether at 19.1 MHz. > > This is such a simple test, though, that _anything_ could be happening within > the processor; for example, the adder might not work at above 16 MHz, or the > like. The test loop doesn't exercise all sides of the processor. So... any > suggestions on how to improve on the tester, and still have a strong visual > clue to whether it works or not?