CLI - Clear Interrupt Mask ;flags(I)
CLI ;I < 0 ;(INH) inherent addressing
Clears the interrupt mask bit in the CCR. When the I bit is clear, interrupts
are enabled. There is a one E-clock cycle delay in the clearing mechanism for
the I bit such that if interrupts were previously disabled, the next instruction
after a CLI will always be executed, even if there was an interrupt pending
prior to the execution of CLI instruction.