Interrupt driven serial routines involve much more overhead as far as program code size and RAM requirements
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This is an actual quote from the pdf file "rs232gd.pdf" found on this site.
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This is my statement and maybe "much" is somewhat of an over statement, it does require "more".

I still challenge that statement.
1) Polled serial gives much more timing constraints.
2) If you can process polled serial fast enough not to require buffering, so can you do interrupt serial, so where is the "more RAM"
3) an interrupt driven serial will require probvably about 20 bytes more of code.

so, you lose NO RAM, 20 bytes of code and gain a total timing independence, so WHER IS THE REASON FRO POLLED?

Erik