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

CHIP-SELECT UNITRegister Name:Register Mnemonic:Register Function:Chip-Select Stop RegisterUCSSP, LCSSP, GCSxSP (x=0-7)Defines chip-select stop address and other controlfunctions.15 0CS9CS8CS7CS6CS5CS4CS3CS2CS1CS0CSENISTOPMEMRDYA1164-0ABitMnemonicBit NameResetStateFunctionMEMRDYBus CycleSelectorBus ReadyEnable1 When MEM is set, the chip-select goes activefor memory bus cycles. Clearing MEM activatesthe chip-select for I/O bus cycles.MEM defines which address bits are used bythe start and stop address comparators. WhenMEM is cleared, address bits A15:6 are routedto the comparators. When MEM is set, addressbits A19:10 are routed to the comparators.1 Setting RDY requires that bus ready be activeto complete a bus cycle. Bus ready is ignoredwhen RDY is cleared. RDY must be set toextend wait states beyond the numberdetermined by WS3:0.NOTE:Reserved register bits are shown with gray shading. Reserved bits must be writtento a logic zero to ensure compatibility with future Intel products. The reset state ofCSEN and ISTOP is ‘1’ for the UCSSP register.Figure 6-6. STOP Register Definition (Continued)The correct sequence to program a non-enabled chip-select is as follows. (If the chip-select is alreadyenabled, either reverse the sequence or disable the chip-select before reprogramming it.)1. Program the START register2. Program the STOP register6-9