hi;
call me crazy.how about a 2 tier architecture?.PC connects to tier1 devices via RS485.say the number is 16.well within 32.tier1 devices can consist of 2 52's.one shall interface with PC other to second tier devices.these 2 52's in tier1 communicate on I2C.each second tier interface of this device can communicate with
32 devices.that gives you 16*32=512 devices.


PC---RS485--'52-I2C-'52 -RS485-'52(32nos)
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16nos


Pranav