У RL78 помимо EI/DI в регистре PSW есть биты ISP0/1, на которые стоит обратить внимание:
In-service priority flags (ISP0 and ISP1)
This flag manages the priority of acknowledgeable maskable vectored interrupts. The vectored interrupt requests specified as lower than the ISP0 and ISP1 values by 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).
