However, if you do happen to choose the DS89C4x0, please don't make the mistake MAXIM's devkit makes, in that it doesn't implement the alternative external addressing mode hardware. It just requires a couple of extra latches beyond what the "usual" external bus interface wants, though there also has to be a means of switching between modes.

With an external CPLD to replace the latches and data buffers, that becomes trivial, but you must provide a means of getting from one mode to another. Likewise, if you want to alter the memory map configuration, there has to be a way to do that.

External memory has to be pretty fast (<70 ns at 12 MHz, and ~15ns at full speed), BTW, so a means for providing a fast external RAM in which the external code can reside is important, and, of course, there has to be a way to move the code into it. The folks who designed the MAXIM evaluation circuit didn't think that through, i.e. they made too many assumptions about what folks would want to do.

There are probably similar issues with other MCU's with "fancy" features. There's no reason why those features can't be given some consideration.

Just my $0.02US worth
(much less than it was before the current administration).

RE