Z80 Interrupts
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Z80 Interrupts
NMI: Interrupts that cannot be turned off via software.
When an NMI is called, the Z80 jumps to a fixed address ($66) and executes the code there until it encounters a RETN command.
The only issue with these is that it is re-entrant. This means that if the code within the NMI is executing and another NMI occurs, the code executing will be interrupted for the new NMI.
This limits the usefulness, however we will only be using this interrupt for a power outage situation, to save the registers and RAM to an SD card.
Mode 0: This interrupt was used for compatibility with the Intel 8080, very popular at the time.
Mode 1: This interrupt works like the NMI where it just jumps to a fixed address. ($38)
Mode 2: This is the most robust of interrupts for the Z80. It allows the interrupting device to place the jump address on the data bus, and even supports prioritization between devices.
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