Lecture 12 Z80 Interrupt 동국대학교 홍유표 1

Y. Hong & E. Lee Polling vs. Interrupt Polling : Periodically check if an event occurs Interrupt : Event sends a signal to CPU 2

Y. Hong & E. Lee Interrupt An hardware-initiated subroutine call or jump that interrupts the currently executing program.  Internal Interrupts : Divide by 0, undefined instruction, …  External Interrupts : Keyboard input, … 3

Y. Hong & E. Lee Multiple Interrupt Sources Typically, there are multiple sources for interrupts CPU should be able to identify who generates the interrupt Also, there must be a way to give priority to interrupt sources 4

Y. Hong & E. Lee Interrupt Source Identification Polling Type  Once an interrupt is received, CPU reads a status register of each device for interrupt generation check. Vector Type  Once an interrupt is received, CPU sends an acknowledge signal (Low on M1 IORQ) to interrupt sources. Then the source sends its ID on data bus. 5

Y. Hong & E. Lee Interrupt Service Routine If an interrupt occurs, after the current instruction is finished an interrupt service routine is called. The interrupt service routine can be in a predefined location. (Mode 1 in Z80) Or, the corresponding routine is placed in the address of I + ID, where I is a interrupt vector register. (Mode 2 in Z80) 6