EXX - Z80 instruction reference

exxExchange register sets 
Swaps BC, DE and HL with BC', DE' and HL', the alternate register set.
1 byte · 4 cycles
Used in Registers, pairs and the shadow setZ80 assembly
 
SZHP/VNC ––––––
Changes no flag
Forms  exx  
Exchanges the 16-bit contents of BC, DE, and HL with BC', DE', and HL'.
         .org 0x8000
        ld bc, 0x0234
        ld de, 0x1000
        ld hl, 0x9000
        exx
        halt