Zilog Z80380 - Manual (Page 109)

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Z380 ™
U SER ' S M ANUAL Z ILOG
DC-8297-03
INDRW
INPUT, DECREMENT AND REPEAT (WORD)
INDRW
Operation: repeat until (BC=0) begin
(HL)
←
(DE)
BC(15-0)
←
BC(15-0) – 1
HL
←
HL – 2
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 DE register is placed on the address bus.
First the BC register, used as a counter, is decremented by one. First the word of data from
the selected peripheral is loaded into the memory location addressed by the HL register.
Then the BC register, used as a counter, is decremented by one. The HL register is then
decremented by two, thus moving the pointer to the next destination for the input. If the result
of decrementing the BC register is 0, the instruction is terminated, otherwise the sequence
is repeated. If the BC register contains 0 at the start of the execution of this instruction, 65536
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 BC is zero; cleared otherwise
H: Unaffected
V: Unaffected
N: Set
C: Unaffected
Addressing Execute
Mode Syntax Instruction Format Time Note
INDRW 11101101 11111010 n X (2+i+w)