《Two-Wire Peripheral Expansion for the AT89C2051 Microcontroller》.pdf

Two-Wire Peripheral Expansion for the AT89C2051 Microcontroller Expanding the The attribute shared by most embedded and memory functions will be accommo- controllers is their ability to interact with dated while not intruding unnecessarily AT89C2051 the outside world. While this fact is gen- on the controller’s limited I/O resources. erally accepted, the form this I/O takes Microcontroller includes everything from parallel and bit- The Evolving Controller addressable digital I/O, analog I/O, as well as complex functions such as a user A well established player in the embed- interface panel. Furthermore, timing ded arena has long been the venerable Application related activities such as pulse width 8051, quite possibly the epitome of an modulation, pulse accumulation, fre- embedded controller. Although this fun- Note quency measurement, and duty cycle damental architecture has been pressed and phase determination are often to serve in a multitude of derivative lumped together under the heading of designs, many of the scaled down ver- high speed I/O. Additionally, while not sions have clearly been limited imple- necessarily I/O related, many small sys- mentations. Worse, most of these have tems will benefit from other functional been plagued by a number of subtle and extensions involving real time clocks, disturbing compatibility issues: almost interval timers, and nonvolatile memo- compatible timers; SFRs, SFR bits, and ries. I/O ports in the wrong places; missing instructions and missing functions. Traditional interface techniques for such peripheral func