Zilog Z80380 Manual de usuario descargar pdf (Pagina 132)

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Z380

™

USER'S MANUAL

DC-8297-03

ZILOG

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)

1 2 ... 127 128 129 130 131 132 133 134 135 136 137 ... 267 268

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Zilog Z80380 Manual de usuario Pagina 132