| IFF1 || 1-bit || Main Interrupt Flip-Flop || Set when interrupts are enabled, cleared on disable.
When the CPU accepts a maskable interrupt, both IFF1 and IFF2 are automatically cleared, inhibiting further interrupts.
On a barebone Amstrad CPC, NMI is not used. So IFF1 and IFF2 values are always identical.
|-
| IFF2 || 1-bit || Stores the state of IFF1 during Non-Maskable Interrupts (NMI) || When an NMI occurs, the processor clears IFF1 to disable interrupts temporarily.
IFF2 stores the previous state of IFF1 so that after the NMI is handled, IFF1 can be restored to its original state.
On a barebone Amstrad CPC, NMI is not used. So IFF1 and IFF2 values are always identical. However, NMI is used by the [[PlayCity]] and [[Play2CPC]] expansions.
|-
| WZ || 16-bit || Internal temporary register pair. Also known as MEMPTR || Used for memory and address calculations.