Zilog Z80380 - Manual (Page 161)

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Z380 ™
U SER ' S M ANUAL Z ILOG
DC-8297-03
OUTD
OUTPUT AND DECREMENT (BYTE)
OUTD
Operation: B
←
B - 1
(C)
←
(HL)
HL
←
HL - 1
This instruction is used for block output of strings of data. 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 fixed port address. The
decremented B register is used in the address.
First the B register, used as a counter, is decremented by one. The byte of data from the
memory location addressed by the HL register is loaded into the selected peripheral. The
HL register is then decremented by one, thus moving the pointer to the next source for the
output.
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
OUTD 11101101 10101011 2+r+o