At 06:40 PM 5/29/97 +1000, you wrote: >Ross has us entralled! I for one must ask: "What on earth are you >going to do with a 4 to 20mA current-encoded panic analog?" > Goes rather against the grain of we "digital types"! I«m not >complaining, you understand, just curious! Have you considered a digital >implementation of the output device? Well, I didn't want to waste the bandwidth, but as long as you are asking . The "client" operates a network of radio linked 4..20 mA input SCADA equipment over a large geographical area. Everything has to be translated to 4..20 mA or a new communications system installed. Their call. > >> I am a newbie to the world of PIC devices having a distant history with >> the 6809 family. > > Hey, that«s aristocracy! By no means a novice! Thank you, . >> There is no synchronisation of serial comms between any of the 4 >> instruments. > > If you intend to interleave the input and output processing, you must >needs use a(n interrupt-driven) state machine UART sampling at three or >four times the bitrate. Err, perhaps I did not explain clearly enough. Each instrument is totally independent of the others. I was simply going to use one PIC per instrument and then combine the digital magnitude output of each before putting the biggest at the input to the DAC. One very simple software design running on each of 4 PICs + 1 magnitude selector software on a 5th PIC. Hope that is clearer .... Your smaller parts count design (1 PIC handling all 4 lines) would involve more complicated coding me thinks ... >> These outputs would then be fed to a small combination of say 4585 4- >> bit magnitude comparators ... > > NOT the way to go! If you«re using one or more PICs, use their logic >to get the maximum. At worst, use four simple DACs and four DIODES to >get the largest. More clever: daisy-chain the PWM pulses from one PIC to >another and let them synchronise so that the final output is the longest >pulse within the fixed cycle time. Clever. >> or should a Basic Stamp version be used? > > Mmmmmm. They have their uses, but performance isn«t one! Candid; thank you. How about some basic code and then using a basic compiler to produce code to load in the PIC? Recommendations? >> 4. Which development machine could be used economically for a >> production of say 10 units? > > The cheapest! See Dontronics. http://www.dontronics.com >... he«s just round the corner (as it were)! Yes. Have found Don McKenzie on the Internet and compared surnames and employment histories. Thanks for your help to date (and everyone else ...) Regards, Ross McKenzie Melbourne Australia