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

CHIP-SELECT UNIT; DATA SEGMENTDATASEGMENT PUBLIC ’DATA’DD 256 DUP (?) ;Reserved for Interrupt Vectors;Place additional memory variable hereDW 500 DUP (?) ;Stack allocationSTACK_TOP LABEL WORDDATAENDS;Program EndsENDExample 6-1. Initializing the Chip-Select Unit (Continued)6.6.2 Example 2: Detecting Attempts to Access Guarded MemoryA chip-select is configured to set an interrupt when the bus accesses a physical address regionthat does not contain a valid memory or peripheral device. Figure 6-11 illustrates how a simplecircuit detects the errant bus cycle and generates an NMI. System software then deals with theerror. The purpose of using the chip-select is to generate a bus ready and prevent a bus “hang”condition.ProcessorNMIGCS5A1158-0AFigure 6-11. Guarded Memory Detector6-20