I don't know the Dallas chip, but if they say it is, then it must be compatible. Yet another issue is the speed of the core. original 8051 is a 12-cycles core, while some other cores are two or even one cycle. This difference must be taken under considration whenever timer/counter block is used to generate some other timings for your program.fireball003 said:Are all the 8051 cores same ? to be precise is Dallas DS89C450 architecture same as other 8051 MCUs?