Zilog Z80380 - Manual (Page 132)

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Z380 ™
U SER ' S M ANUAL
DC-8297-03
Z ILOG
LDDR
LOAD, DECREMENT AND REPEAT (BYTE)
LDDR
Operation: repeat until BC=0 begin
(DE)
←
(HL)
DE
←
DE – 1
HL
←
HL – 1
BC(15-0)
←
BC(15-0) – 1
end
This instruction is used for block transfers of strings of data. The bytes of data at the location
addressed by the HL register are loaded into memory starting at the location addressed by
the DE register. The number of bytes moved is determined by the contents of the BC register.
If the BC register contains zero when this instruction is executed, 65,536 bytes are
transferred. The effect of decrementing the pointers during the transfer is important if the
source and destination strings overlap with the source string starting at a lower memory
address. Placing the pointers at the highest address of the strings and decrementing the
pointers ensures that the source string is copied without destroying the overlapping area.
This instruction can be interrupted after each execution of the basic operation. The Program
Counter value of the start of this instruction is saved before the interrupt request is
accepted,so that the instruction can be properly resumed.
Flags: S: Unaffected
Z: Unaffected
H: Cleared
V: Cleared
N: Cleared
C: Unaffected
Addressing Execute
Mode Syntax Instruction Format Time Note
LDDR 11101101 10111000 n X (3+r+w)