NEC switch - Manual (Page 41)

CHAPTER 3 CPU ARCHITECTURE
User’s Manual U12978EJ3V0UD
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(a) Interrupt enable flag (IE)
This flag controls interrupt request acknowledgment operations of the CPU.
When 0, the IE flag is set to the interrupt disabled status (DI), and interrupt requests other than non-
maskable interrupts are all disabled.
When 1, the IE flag is set to the interrupt enabled status (EI). Interrupt request acknowledgment enable is
controlled by the interrupt mask flag corresponding to each interrupt source.
The IE flag is reset (0) upon DI instruction execution or interrupt acknowledgment and is set (1) upon EI
instruction execution.
(b) Zero flag (Z)
When the operation result is zero, this flag is set (1). It is reset (0) in all other cases.
(c) Auxiliary carry flag (AC)
If the operation result has a carry from bit 3 or a borrow at bit 3, this flag is set (1). It is reset (0) in all other
cases.
(d) Carry flag (CY)
This flag stores overflow and underflow upon add/subtract instruction execution. It stores the shift-out
value upon rotate instruction execution and functions as a bit accumulator during bit manipulation
instruction execution.