LDIR - Z80 instruction reference

ldirLoad, increment and repeat 
Copies BC bytes from (HL) to (DE), incrementing both, until BC is zero.
2 bytes · 21/16 cycles·21 cycles for a pass that repeats, 16 for the last
Used in The Z80 instruction setZ80 assembly
 
SZHP/VNC ––000–
0 always 0
– not changed
Forms  ldir  
Transfers a byte of data from the memory location pointed to by HL to the memory location pointed to by DE. Then HL and DE are incremented and BC is decremented. If BC is not zero, this operation is repeated. Interrupts can trigger while this instruction is processing.
         .org 0x8000
        ld hl, source
        ld de, 0x9000
        ld bc, 4
        ldir
        halt
source: .byte 1, 2, 3, 4