> This is my (slightly
> educated) guess about why it exists: banking and paging make 
> the hardware
> more simple. Someone else may have some evidence for or 
> against this idea,
> but for what little bit of digital design I remember this is 
> my stand. ;)

Main reason is that the (data or code) address field must fit in an
instruction, an instruction has a limited size, and this size should not
be choosen too large because the Flash is a large part of the cost
(size) of the chip. Another: some PICs have an address range that is
large than the register size (8 bit).

Note that in a sense even an ARM has some sort of paging/banking:
neither 32-bit constants, nor full 32-bit data or code (same thing on an
ARM) addresses fit into a (32 bit!) instruction. So there are tricks and
workarounds to get a 32-bit value in a register, and to address anything
in the 32-bit address space (but not paging/banking as we know it on the
PICs).

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu
 

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