Hi John,

((And then how are we going to emulate the internal comparators of the AT89C2051, AT89C4051, which are very popular and cheap.))


Since several years I built an AT89c2051/2041 emulator using an AT89c52, an external rail-to-rail CMOS comparator and a serial 4K ROM simulator.
An AT89c2051 uses only P1 and P3 so we can use P0 and P2 of an AT89c52 for an external serialy downloadable RAM . It works fine. It is only a little difference because P1.0 and P1.1 are not open drain in an AT89c52 but for the big majority of applications it is insignificant.
I also think for this kind of small ROM processor (2k..4k) it is not necessary to have such luxury tools like break points.
As a matter of fact the hole processes of compiling, linking, serial downloading and starting takes less then 0.5 seconds on an old 150Mhz Pentium running a DOS window in WIN89.
So I put break points directly in the source code and I change them very fast for debugging purposes.

Regards,
Cristian