ST486SMM Datasheet PDF - STMicroelectronics

Introduction
This Programmer’s Guide has been written to aid programmers in the creation of software using the SGS-Thomson System Management Mode (SMM) for ST486DX CPUs. This guide should be used in conjunction with the SGS-Thomson ST486DX and ST486DX2 Processors Data Book. SMM programming related to the ST486SLC/e is covered in the ST486SLC/e SMM Programmer’s Guide.

SMM provides the system designer with another processor operating mode. Within this document the standard x86 operating modes (real, v86 and protected) are referred to as normal mode. Normal mode operation can be interrupted by an SMI interrupt or special instruction that places the processor in System Management Mode (SMM). SMM can be used to enhance the functionality of the system by providing power management, register shadowing, peripheral emulation and other system level functions. SMM can be totally transparent to all application software, including protected mode operating systems.