Zilog Z80380 Bedienungsanleitung PDF herunterladen (Seite 108)

5-74

Z380

™

USER'S MANUAL

DC-8297-03

ZILOG

INDR

INPUT, DECREMENT AND REPEAT (BYTE)

INDR

Operation: repeat until (B=0) begin

(HL) ← (C)

B ← B – 1

HL ← HL – 1

end

This instruction is used for block input of strings of data. The string of input data from the

selected peripheral is loaded into memory at consecutive addresses, starting with the

location addressed by the HL register and decreasing. During the I/O transaction the

32-bit BC register is placed on the address bus. Note that the B register contains the loop

count for this instruction so that A15-A8 are not useable as part of a fixedport address.

First the byte of data from the selected peripheral is loaded into the memory location

addressed by the HL register. Then the B register, used as a counter, is decremented by

one. The HL register is then decremented by one, thus moving the pointer to the next

destination for the input. If the result of decrementing the B register is 0, the instruction is

terminated, otherwise the sequence is repeated. If the B register contains 0 at the start of

the execution of this instruction, 256 bytes are input.

This instruction can be interrupted after each execution of the basic operation. The Program

Counter value at 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: Set if the result of decrementing B is zero; cleared otherwise

H: Unaffected

V: Unaffected

N: Set

C: Unaffected

Addressing Execute

Mode Syntax Instruction Format Time Note

INDR 11101101 10111010 n X (2+i+w)

1 2 ... 103 104 105 106 107 108 109 110 111 112 113 ... 267 268

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Zilog Z80380 Bedienungsanleitung Seite 108