RETN - Z80 instruction reference

retnReturn from non-maskable interrupt 
Returns from a non-maskable interrupt routine by popping PC and copying IFF2 into IFF1.
2 bytes · 14 cycles
SZHP/VNC ––––––
Changes no flag
Forms  retn  
Used at the end of a non-maskable interrupt service routine (located at 0066h) to pop the top stack entry into PC. The value of IFF2 is copied to IFF1 so that maskable interrupts are allowed to continue as before. NMIs are not enabled on the TI.
         .org 0x8000
        retn
        halt