# Block write to port

$$\begin{rcases} (C) \longleftarrow (HL)\\HL \longleftarrow HL+1 \text{ if } D = 0\\HL \longleftarrow HL-1 \text{ if } D = 1\\B \longleftarrow B-1 \end{rcases} \text{repeat while } L=1 \And B \not = 0$$

76543210
11101101ED
101LD011

D 0=Increment, 1=Decrement HL after each iteration

L If set then if $$B \not = 0$$ then $$PC \longleftarrow PC-2$$ so that the instruction is repeated.

The contents of Register C are placed on the bottom half (A0…A7) of the address bus to select the I/O device at one of 256 possible ports.

Register B can be used as a byte counter, and its contents are placed on the top half (A8…15) of the address bus at this time.

Then one byte from the address pointed to by HL is placed on the data bus and written to the port.

Finally, the byte counter is decremented and register pair HL is incremented.

##### Flags Affected
Flags
 - z - - - - n -
zset if B = 0, always true for repeat operations
nset
##### Opcode Matrix
IncrementDecrement
Single
OUTI
EDA3216
OUTD
EDAB216
Repeat
OUTIR
EDB3221
OUTDR
EDBB221
 Instruction Opcode hexSize bytesCycle count Special