80C186EB/80C188EB Microprocessor User's Manual - CEUNES

OVERVIEW OF THE 80C186 FAMILY ARCHITECTUREFFFFFHABData:DS:BCCode:CS:EStack:SS:HDExtra:ES:JEFGHJIK0HA1037-0AFigure 2-7. Currently Addressable SegmentsThe segment register is automatically selected according to the rules in Table 2-2. All informationin one segment type generally shares the same logical attributes (e.g., code or data). This leads toprograms that are shorter, faster and better structured.The Bus Interface Unit must obtain the logical address before generating the physical address.The logical address of a memory location can come from different sources, depending on the typeof reference that is being made (see Table 2-2).Segment registers always hold the segment base addresses. The Bus Interface Unit determineswhich segment register contains the base address according to the type of memory referencemade. However, the programmer can explicitly direct the Bus Interface Unit to use any currentlyaddressable segment (except for the destination operand of a string instruction). In assembly language,this is done by preceding an instruction with a segment override prefix.2-11