Editing Zilog Z80 (section)

=== Example code ===
The following Z80 assembly source code is for a subroutine named <code>memcpy</code> that copies a block of data bytes of a given size from one location to another. Important: the example code does not handle the case where the destination block overlaps the source; a serious limitation, but one that is irrelevant for some applications—such as, especially, when the source is in ROM and the destination in RAM, so they can never overlap. The data block is copied one byte at a time, and the data movement and looping logic utilizes 16-bit operations. It demonstrates a variety of instructions but in practice it would not be coded this way as the Z80 has a single instruction that will replace this entire subroutine: <code>LDIR</code>. The sample code will move one byte every 46 T-states. Substituting the <code>LDIR</code> instruction will move each byte in only 21 T-states. Note that the assembled code is binary-compatible with the Intel 8080 and 8085 CPUs.

{|
|-valign="top"
|<syntaxhighlight lang="text" highlight="16">

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1000
 1000
 1000 F5
 1001 7E
 1002 12
 1003 23
 1004 13
 1005 0B
 1006 78
 1007 B1
 1008 C2 01 10
 100B F1
 100C C9
 100D
</syntaxhighlight>
|<syntaxhighlight lang="tasm" highlight="16">
 ; memcpy --
 ; Copy a block of memory from one location to another.
 ; This routine is the equivalent of LDIR
 ;
 ; Entry registers
 ; HL - Address of source data block
 ; DE - Address of destination data block
 ; BC - Number of bytes to copy
 ;
 ; Return registers
 ; HL - First byte after source data block
 ; DE - First byte after destination data block
 ; BC - Zero
 ; (LDIR does not fully save AF. H, P/V, and N are reset.)

             org     1000h       ; Origin at 1000h
 memcpy      public
             push    af          ; Save AF like LDIR
 loop        ld      a,(hl)      ; Copy 1 source byte
             ld      (de),a      ; to its destination
             inc     hl          ; Bump source pointer
             inc     de          ; Bump dest pointer
             dec     bc          ; Count the copied byte
             ld      a,b         ; Test BC for zero
             or      c           ; If BC != 0,
             jp      nz,loop     ; repeat the loop
             pop     af          ; Restore AF
             ret                 ; Return
             end
</syntaxhighlight>
|}