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

INTERRUPT CONTROL UNITRegister Name:Register Mnemonic:Register Function:Poll Status RegisterPOLLSTSRead to check for pending interrupts when polling15 0IREQVT4VT3VT2VT1VT0A1209-A0BitMnemonicBit NameResetStateFunctionIREQInterruptRequest0 This bit is set to indicate a pending interrupt.VT4:0 Vector Type 0 Contains the interrupt type of the highestpriority pending interrupt.NOTE:Reserved register bits are shown with gray shading. Reserved bits must be writtento a logic zero to ensure compatibility with future Intel products.Figure 8-12. Poll Status Register8.3.7 End-of-Interrupt (EOI) RegisterThe End-of-Interrupt register (Figure 8-13) issues an End-of-Interrupt (EOI) command to the InterruptControl Unit, which clears the In-Service bit for the associated interrupt. An interrupt handlertypically ends with an EOI command. There are two types of EOI commands: nonspecificand specific. A nonspecific EOI simply clears the In-Service bit of the highest priority interrupt.To issue a nonspecific EOI command, set the NSPEC bit. (Write 8000H to the EOI register.)A specific EOI clears a particular In-Service bit. To issue a specific EOI command, clear theNSPEC bit and write the VT4:0 bits with the interrupt type of the interrupt whose In-Service bityou wish to clear. For example, to clear the In-Service bit for INT2, write 000EH to the EOI register.The timer interrupts share an In-Service bit. To clear the In-Service bit for any timer interruptwith a specific EOI, write 0008H (interrupt type 8) to the EOI register.8-21