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CHAPTER 2 REGISTER
(1) Interrupt enable flag (IE)
This flag controls interrupt request acknowledge operations of CPU.
When IE = 0, the IE is set to interrupt disable (DI), and interrupts other than non-maskable interrupts are
all disabled.
When IE = 1, the IE is set to interrupt enable (EI), and an interrupt request acknowledge is controlled with
an in-service priority flag (ISP), an interrupt mask flag for various interrupt sources, and a priority
specification flag.
This flag is reset (0) upon the DI instruction execution or interrupt request acknowledgment and is set (1)
upon execution of the EI instruction.
(2) Zero flag (Z)
When the operation result is zero, this flag is set to (1). It is reset to (0) in all other cases.
(3) Register bank select flags (RBS0 and RBS1)
These are 2-bit flags to select one of the four register banks.
In these flags, the 2-bit information which indicates the register bank selected by SBL RBn instruction
execution is stored.
(4) Auxiliary carry flag (AC)
If the operation result has a carry from bit 3 or a borrow at bit 3, this flag is set to (1). It is reset to (0) in
all other cases.
(5) In-service priority flag (ISP)
This flag manages the priority of acknowledgeable, maskable vectored interrupts. When ISP = 0, vectored
interrupt requests specified to the low level with the priority specification flag register (PR) are disabled
for acknowledgment. Actual acknowledgment for interrupt requests is controlled by the state of the interrupt
enable flag (IE).
(6) 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.