ItnRODUClION This chapter discusses the subsystem functions of the 486 system that are of interest to a system programmer. First an overview of the function is provided, then any programmable characteris- tics are discussed followed by addressing and register informa- tion for that function. As identified in the previous chapter, the main subsystems of the 486 are the CPU board and the Hard Disk Controller board. CEftRAL PROCESSIS UNIT (CPU) HARDWARE OVERVIEW The Central Processing Unit (CPU) printed circuit board performs most of the major functions for the 486 system. Refer to Figure 5-1.
The CPU printed circuit board is designed around two major sections of hardware, the 80186 section and the Z-80A section. Within the 186 section are the 186 microprocessor, the floppy disk controller, the boot ROM, the main memory, the memory management unit, the parallel interface controller (8255), and programmable interrupt controller (8259) IC chips. 5-1