At 06:10 PM 7/21/99 -0700, you wrote: >William K. Borsum wrote: >> >> Greetings: >> I've been following the PIC to FDC conversations a bit, and have a related >> question: >> >> I have an application where I need to log data at the rate of up to 200 >> K-bytes per second, to a depth of 120-160 Mega-bytes. >> Part of the problem is that it is memory is broken up into a series of ring >> buffers that are sequentially over-written till an event occurs, so flash >> or eeProm with a short finite life--or holes in the memory because of bad >> blocks--won't work. Only viable alternative I've come up with is sRam, but >> the largest chips only appear to be 512Kx8, which means 200+ chips to get >> the total memory I need. Oh yes--environment sees shock and vibration to >> 100+ G's, and the whole thing needs to fit in a can about 3.5" in diameter. >> >> Question: does anyone have a sneaky alternative that will work--like a >> micro-hard drive that will survive? If so, how would the interface work? >> Has anyone implemented an IDE interface, or interface to a sRAM PCMCIA card >> on a PIC? >> >> Kelly > > sRam in PCMCIA form is *hideously* expensive, about $133 for a 4Mb >card, and you don't often SEE larger SRam cards than 4Mb. 40 of those >wouldn't be a good answer for you, I'd assume! > > Now a laptop (or 1.7" PCMCIA) HDD, that's a possibly do-able answer, >and more like $15-$20 for a 200Mb or so laptop HDD. About 1 year >service life (if you leave the drive motor spinning constantly), shock & >vibration are a potential problem but these drives do handle some decent >forces (I suspect if you sprung it inside the can, with a little added >mass & some air damping or something, you could make it work, MAYBE - >depends on the amplitude of the vibrations.) > > Also, PCMCIA Flash Cards might be do-able (Sandisk makes 175Mb and >larger cards), except they'd get worn out by your application, right? >Same for laptop Flash drives (SanDisk makes these, act just the same as >regular laptop drives but they wear out after lots of writes.) > > Have you considered a set of battery-backed 72-pin SIMMs, or one or >two DIMM memory modules? Seems to me that using that setup may be a >really good answer for you here (The storage media's fairly cheap, data >bandwith's NOT a problem, etc.) Could sample the data to a PCMCIA drive >for downloading, or some such, perhaps. That might be good (you'll want >a GOOD socket that's not going to vibrate loose, though these types of >sockets should be OK, I'd think - maybe tape the metal latches in place >to prevent any possible shaking loose of the RAM PCB's.) I'd wonder if >DIMMs would stay in place well, here, have to help them stay in place >I'd think Flash in any form will not work for the ring-buffer applications--just gets over-written too many times too quickly. Also, don't want to deal with the holes, memory management issues, etc. I would like to hear from anyone with mini-hdd experience. Yes, I can isolate the drive from shock and vibration to a certain extent--don't know the profile yet. Also, IDE interface management issues--has anyone done a PIC-IDE interface and is the code available? Simm's and Dimm's--possible--but are they available in sRAM? If so, from whom? and in reasonable chunks that can be built up into the 100+ Megabyte range? Again, the problems associated with normal dRAM and its power consumption, refresh, etc. may be too much for this project. The data is very costly to acquire and any risk of loss is too much. I also have volume and weight limits on the batteries--but would consider it if there were dRAM controllers that could handle all of the memory management functions in hardware and be totally transparent to the the Pic. Anyone have any experience along these lines?? Kelly **************************************************************************** ******** All legitimate attachments to this email will be clearly identified in the text. William K. Borsum, P.E. OEM Dataloggers and Instrumentation Systems &